You’re a good Mum. Having a baby is hard work as there’s a lot of sleep deprivation that makes the anxiety worse but you’ve sought help and that’s a good thing.
I was the same with my first baby, when she was asleep I used to think she looked like she wasn’t breathing and so I’d wake her up to reassure myself

.
Don’t stress about the feeding. I breastfed and was told by a horrible health visitor that baby wasn’t gaining enough weight and that I needed to cook myself a full English breakfast

another health visitor told me to ignore her.
If breastfeeding is not working for you then switch to bottle feeding.
Try to relax and just do your own thing. Don’t worry too much about what other mothers do and hopefully the medication will help but bear in mind it can take 6 weeks to kick in.