He noticed a smell but did not feel any wind coming out of him
Question

                I am affected by waswaas (whispers from the Shaytaan) and I am trying hard to avoid doubts that come to me regarding wudoo’ and prayer.

But two days ago, when I was praying in the mosque, I suddenly noticed a smell (of passing wind), even though I did not feel anything in my stomach, and I did not feel that anything came out of me before I noticed the smell. 

I said: This is waswaas, and I completed my prayer. But after I had prayed, I began to strongly doubt the validity of my prayer. Perhaps there had been some movement in my stomach and I had forgot, or perhaps it was gas, because that happens to me sometimes. 

I still have my doubts until now. 

Is my prayer valid, or should I make it up? Do I have to do anything, because several days have passed since I offered that prayer?
Praise be to Allah.
    Your prayer is 
    valid and you do not have to repeat it; do not worry about the smell that 
    you noticed so long as you did not feel anything coming out of you. You 
    should not pay attention to the waswaas that comes to your mind and cast 
    aside the doubts that cross your mind. 

    With regard to the 
    hadeeth which says that a man complained to the Prophet (blessings and peace 
    of Allah be upon him) that he felt something during the prayer, and asked 
    whether he should stop praying, and he said: “No, unless you hear a sound or 
    notice a smell” (narrated by al-Bukhaari, 20546; Muslim, 361), this has to 
    do with one who feels something and is not sure whether it came out; this 
    indicates that one should not do something that is due to waswaas, because 
    the certainty of being in a state of purity cannot be affected by 
    uncertainty or doubt. 

    Shaykh Ibn Baaz 
    (may Allah have mercy on him) said: 

    The believer 
    should not pay attention to this waswaas, because this will encourage the 
    Shaytaan, and the Shaytaan is keen to spoil the good deeds of the sons of 
    Adam, such as prayer and so on. What he must do is be aware of his tricks 
    and whispers, put his trust in Allah, and assume that whatever happens of 
    waswaas is from the Shaytaan, so that he will not pay any attention to it. 
    Then if something comes out of him and he is certain of it, not uncertain, 
    he should clean himself again (istinja’) and repeat wudoo’. But so long as 
    there is any uncertainty, even if it is slight, then he should not pay 
    attention to that, and he should still believe that he is in a state of 
    purity and ward off the whispers of the Shaytaan.

    End quote from 
    Majmoo‘ Fataawa Ibn Baaz, 10/123

    And Allah knows 
    best.