Breast feeding, formula feeding, and chronic pain

I'm (sort of)* a FTM due on January 7th. I've dealt with slowly progressive chronic pain in my feet since early childhood. Since becoming pregnant I've been unable to take the supplements that help me function day to day, but regularly tell myself the end result will be worth it. This last week or so has been particularly bad, such that I'm unable to manage without forearm crutches. I know part of that is weight gain, which should improve once he's born. However, I still won't be able to resume my normal supplement routine until we stop breast feeding. Right now I feel like I can't cope with that. I was planning on breast feeding for three months, then weaning and taking supplements again. Right now I'm at the end of my rope and feeling like we should just start with formula, but it seems like to advantages to him and me of going through at least 6 weeks are real.

I don't know what I'm looking for. I guess advice from those who have done both?

*I've fostered an infant and a toddler before but never had the option of breast feeding, clearly.