Whoever voluntarily swallows food remnants that are caught between his teeth, or swallows some of the water he uses to rinse out his mouth whilst doing wudoo’, has broken the fast
Question

I used to suffer from persistent insinuating thoughts, and when I did wudoo’ in Ramadan, I would spit excessively for fear that some of the water would go down my throat. One time I lost my nerve, and I swallowed water deliberately. How can I offer expiation for my sin?
On one occasion I was sleeping, and my mother was drying almonds and she put them beside me in Ramadan, and I felt something in my mouth and I do not know whether it was food remnants in my mouth or almonds, so I swallowed it because I was too lazy to get up and rinse out my mouth. What should I do?
Another time in Ramadan there was a little bit of wudoo’ water left in my mouth and I swallowed it deliberately.
Finally, what is the ruling on one brings up a little vomit then swallows it, because he is too lazy to get up and rinse out his mouth?
Now I am breastfeeding, and I have repented to Allah. How can I expiate for my sin?
Praise be to Allah.Firstly:
If the fasting person rinses out his mouth, he must spit out the water, and it is not prescribed for him to spit a great deal after rinsing out his mouth. This is a bad habit that leads to waswaas (whispers from the Shaytaan) and doubt concerning one’s acts of worship.
Please see the answer to question no.  49005
Secondly:
With regard to your saying “One time I lost my nerve, and I swallowed water deliberately”:
– If you are telling the truth that you swallowed water from rinsing your mouth that was still in your mouth, or some of it, then you broke your fast, so you have to repent and make up that day.
– If you meant that you swallowed saliva after rinsing out your mouth and spitting out the water that was in your mouth, then you do not have to do anything.
Al-Bujayrimi (may Allah have mercy on him) said:
Swallowing saliva after rinsing out one’s mouth does not matter, even if it is possible to  spit it out, because it is difficult to avoid that. End quote.
Similarly, with regard to your saying “there was a little bit of wudoo’ water left in my mouth and I swallowed it deliberately”:
– If this was water left after rinsing out your mouth, then you did invalidate your fast and you have to make it up.
– If there was wetness in the mouth after rinsing it out and spitting out the water, then the more correct view is that you do not have to do anything.
Thirdly:
If a person voluntarily swallows remnants of food that are left between his teeth when it is possible to spit them out, then he invalidates his fast by doing that. But if he swallows them involuntarily, such as if they reached his throat with his saliva and he was not able to expel them, then his fast is valid and he does not have to do anything.
Please see the answer to question no.  78438.
What appears to be the case from what the questioner said is that she deliberately swallowed food remnants that were in her mouth, and she was too lazy to get up and clean them out of her mouth. If that happened at night, then she does not have to do anything further, but if that was after dawn had broken, then she has to make up that day and repent to Allah.
Fourthly:
If a person vomits involuntarily, then he does not have to do anything further and his fast is still valid but if he vomits deliberately, then he has to make up that day.
Please see the answer to question no.  95296.
If he vomits then swallows it, if he did not do that deliberately, then he does not have to do anything further. But if he swallowed it deliberately, then he has invalidated his fast and he has to make up that day. The scholars of the Standing Committee said:
If he vomited deliberately, then he has invalidated his fast. If he could not help vomiting, then he has not invalidated his fast. Similarly, it is not invalidated if he swallows it, so long as he did not do that deliberately.
Fataawa al-Lajnah ad-Daa’imah (10/254)
For more information, please see the answer to question no. 115155
Conclusion:
What you have to do is make up the days on which you invalidated the fast deliberately, whether that was by swallowing water that was in your mouth, other than saliva, swallowing which does not invalidate the fast, or by swallowing what remained in your mouth of food, or what reached it of vomit. So work out the number of such days, and make up those fasts, and also repent to Allah, may He be glorified and exalted, for what you did of such things voluntarily.
But you only have to make up those days when your period of breastfeeding is over. As for the woman who is breastfeeding, she does not have to make up fasts that she owes whilst she is still breastfeeding, if that is too difficult for her, or she fears for herself or her child if she fasts whilst she is breastfeeding.
With regard to severe waswaas and feeling stressed out, we hope that you are not to be blamed for that. But you have to focus on getting rid of that waswaas and not paying any attention to it. The best remedy for waswaas is to ignore it and not pay any attention to it, and not to think of it.
For more information on remedies for waswaas please see the answer to question no. 60303
And Allah knows best.