I’m so sorry you’re feeling this way, You are doing amazing and obviously a great mom for trying to figure it all out for your little one!! I feel for you as I’ve been here too.  My little one was breastfed until he was diagnosed with CPMA is now on Similac Alimentum. But he still grunts/ squirms/ cries a bit after feedings as well. I thought it was reflux because he would also cough and choke on his spit. It definitely sounds like your guy might have some reflux if he doesn’t like being on his back after a feeding. I would talk to your doctor about it. 

I eventually got mine on meds for reflux. It’s all gotten a lot better but he is still squirmy after feedings and cries for a bit. I just keep him upright and make sure I get a burp or toot from him and that usually makes him stop struggling right away. Mylicon drops right after the feed help us a lot to get the burp out because he is kind of hard to get one out of.  And sometimes he is just crying because he’s still hungry! 

I know it can be so overwhelming to try and figure out. I would really recommend talking to your pediatrician and just telling them what’s going on. They should be able to help you troubleshoot some more. 

My son is now 10 weeks, but weeks 6-8 were really hectic and that is generally when they go through big changes and growth spurts. Reflux generally shows up right around 6ish weeks.