Ahhh Melanie, I haven't been in the same situation as you exactly but I can relate.
I had problems BFing and went to expressing but gave that up around the two month mark. I felt awful but it really was the best thing for me to do (long story).
I also had a condition called SPD (unstable pelvis) and was unable to walk, stand or bend without being in pain for six months after
DD was born. So I know what being debilitated feels like and when everything you need to do for your baby actually causes you physical pain. One of the reasons I gave up expressing was that I basically couldn't get out of the house to get to physio appointments and actually could have avoided being in pain so long if I'd stopped expressing sooner.
I guess, in hindsight, I would say that your physical health has to be absolutely paramount because if you're in pain it affects your mental health too and that can impact your relationship with your
DH and your child.I know it's a cliche and it really took a long time for me to realise how true it is, but happy mummy really does equal happy baby.
In my case, I felt guilty for two main reasons. Firstly, I felt like a failure because I had wanted to BF very much and when they're so little, so much of looking after them revolves around feeding that I felt like I was failing
DD.
Secondly, I felt guilty because I was aware of the health benefits of BFing and thought that it would be my fault, essentially, if she got sick.
Both these reasons/feelings have faded with time. I spoke to a lovely woman at the ABA who could tell how distraught I was and the best thing she said to me was, "being a good mum is about so much more than breastfeeding." That was absolutely the best thing that anyone could have said to me. As your baby gets older, this becomes so true too because you are interacting with them so much more and for me, being a good mum became less about BFing or FFing but about how I played with her, where I took her, how I settled her etc. etc.
And as far as my worries about her health went, well she's had one trip to the doctor in 17 months which is far less than most babies I know.
Your post brought back memories for me of how I felt all those months ago but please take heart that it does get easier and you might find it helpful to write a letter to yourself explaining your reasons. Just so you can look back on it in the weeks to come and realise that you're making the best decision you can with all the facts to hand.
As someone else suggested though, I would see another opinion re the medication and make doubly sure that there isn't anything you can take that will still make it possible to BF.