One should not exaggerate in cleaning oneself after relieving oneself
Question

I have a serious problem when purifying myself from major impurity, because I purify myself with a little water, then I wipe myself sometimes 21 times and sometimes more than that, yet I still see traces, which makes me purify myself again with water. Hence I spend a long time in the washroom in order to cleanse myself, which has damanged my health. What is your opinion? Is there a specific number of times for wiping oneself in order to become pure?.
Praise be to Allah.Firstly: 
The phrase major impurity applies to janaabah (impurity following sexual activity), menses and nifaas (postpartum bleeding). The way to purify oneself from that is: the woman should start by cleaning her private parts, then makes the water reach all parts of her body. That is explained in the answer to question 10790. With regard to the emission of wind, urine, stools and madhiy (prostatic fluid), this is minor impurity, and perhaps this is what you are referring to. 
The scholars of the Standing Committee for Issuing Fatwas said: Minor impurity is that which necessitates wudoo’ but not ghusl, such as the emission of urine, stools and wind from the back passage, eating camel meat, and sleeping. 
As for major impurity, it is that which necessitates ghusl, such as intercourse and ejaculation as the result of desire, as in the case of a wet dream or otherwise, or menses or postpartum bleeding.'(Fatawa al-Lajnah al-Daa’imah, vol. 3, 4/112). 
Secondly: 
Istijmaar or wiping oneself means removing impurity on both passages, front and back, with a stone or a tissue and the like. 
What is required in istijmaar is that the number of wipes should be no less than three, and to achieve purity, which is the removal of the impurity and making the place dry. The sign that purity has been attained is that the last wipe should come back dry with no trace of impurity on it. And if that is done, then the purpose has been fulfilled and the place has become pure. 
Muslim (262) narrated from Salmaan (may Allah be pleased with him) that he said: Our Prophet (blessings and peace of Allah be upon him) forbade us to clean ourselves with less than three stones. 
Ibn Qudaamah said in al-Mughni (1/102): 
Both things are stipulated together: purification and completing three; one of them done without the other is not sufficient. This is the view of al-Shaafa’i and a number of others. End quote. 
The scholars of the Standing Committee for Issuing Fatwas were asked: If men use stones to clean the back or front passage, how can women clean the front passage when there is no water? 
They replied: Cleaning oneself with stones or whatever takes their place, apart from bones and dung, takes the place of cleaning oneself with water when purifying the front and back passage. Men and women are the same in that regard. What is required is three clean stones for both back and front. If that is not sufficient, then it is essential to do more until it becomes clean. It is best to make it an odd number, so if it becomes clean after four wipes, it is prescribed to do a fifth, and if it becomes clean after six, it is prescribed to do a seventh, because of the general meaning of the words of the Prophet (blessings and peace of Allah be upon him): “Whoever cleans himself, let him make it an odd number.”(Fatawa al-Lajnah al-Daa’imah, vol. 2, 4/36)
But if what you mean by istijmaar is washing the traces of impurity with water, no number is stipulated in this case, and what is required is to wash off the impurity until you think that it has most likely been removed. In this case it is sufficient to act upon what you think is most likely, and it is not stipulated that you should be certain that it has been removed. 
You should note that this exaggeration comes from the waswaas or whispers of the Shaytaan, who intends thereby to make worship difficult for the Muslim so that he will give it up or his life difficult and make him fall into distress and grief. 
You have to limit yourself to that which is mentioned in sharee’ah without adding or taking away anything. If the shaytaan whispers to you that you have not purified yourself, do not pay any attention to this whisper, until Allah takes it away from you. 
Shaykh Ibn Baaz (may Allah have mercy on him) said: For a believer must be an enemy of the shaytaan, fighting him and resisting him, and not giving in to him. If he tells you that you did not do wudoo’ and did not pray, when you know that you did do wudoo' and pray, and you can see water on your hand and you know that you prayed, then do not pay any heed to the enemy of Allah, and affirm to yourself that you have prayed and be certain that you have done wudoo’, and do not repeat any of that. Seek refuge with Allah from the enemy of Allah, the Shaytaan. Thus the believer must be strong in fighting the enemy of Allah and resisting him so that he will not gain any power over him or harm him, because if he gains power over a person he will make him like one who is insane and will toy with him. So what the believer, man or woman, must do is beware of the enemy of Allah, seek refuge with Allah from his evil and his tricks, and be strong and patient in doing so, so that he will not obey him by repeating the prayer or by repeating wudoo' or by repeating the takbeer and so on. 
Similarly, if he says to you: Your garment is impure, or this spot is impure, or there is some impurity in the bathroom, or there is some impurity on the ground that you walked on, or there is such and such in the place where you pray, then do not obey him in that. The enemy of Allah is lying. Seek refuge with Allah from his evil and pray in the place where you usually pray and on the mat on which you usually pray and on the ground that you walk on, and know that it is clean and pure, unless you see with your own eye some impurity that you stepped on when it was still wet, in which case wash your foot. And praise be to Allah. 
With regard to his whispers, do not pay any heed to the enemy of Allah. Remember that the basic principle is that things are pure. This is the basic principle, so do not pay any heed to the enemy of Allah unless you are certain that you have seen it with your own eyes, so that the enemy of Allah will not gain any power over you. We ask Allah to keep us all safe and sound."(Fatawa Noor ‘ala al-Darb, 1/77. 78 )
We ask Allah to guide you and help you to do all that is good. 
And Allah knows best.