TMI post, looking for help!

This post is about digestive issues so if you are sensitive dont click please! For the last year or so I have had digestive issues. It started when I found out I was pregnant with my second son. I started not pooping for a week or longer and then would randomly have explosive diarrhea, then right back to not pooping. I tried going gluten free, vegan, and cutting out anything that I thought was causing it. During my pregnancy, it seemed that potatoes were causing it so I cut them out and it helped a little bit. But now a month postpartum, I havent touched a potato in months and my stomach is worse than ever! Every time I'm able to go to the bathroom its diarrhea and extremely painful, both in my stomach and on my rear end, it feels like acid coming out. I just wish I could go once a day like normal and not have it build up for a week before exploding.. ugh, any ideas what's wrong?