hi R.!
my little emma was really hard to burp too! i would really worry about it, but someone told me (i think my pediatrician) that she may not burp and that's ok. if they seem uncomfortable, then you can try again, but you may not want to force it cause it might cause them to spit up unnecessarily. as far as the formula, emma had to be on nutramigen, too, but we found that similac enfamil worked better for her. they're exactly the same thing, just a different brand. i think they're the same price too. you might try that and see if it helps. also, emma always ate a lot! when she was really little, like a few weeks, she would eat at least 4 oz. and everyone told me she should only be eating 2-3 oz.! i worried that i was over-feeding her, but she was still hungry! i quickly learned that emma wouldn't over-eat. she spit on the bottle or pulled off my breast when she was done and wouldn't take anymore. babies know when they're full, no matter what other people say... at least mine always has. she quickly went from eating 4 oz. at a time, to 5-6 oz. and now she eats anywhere from 6-8 oz... she's 10 months old.
i really think you can rest in the fact that your babies are going to be able to tell you when they're done eating. if they're still hungry, let them eat. my doctor always said the main concern for little ones was gaining weight... not how much they were gaining... unless its way unhealthy. but it doesn't sound like you're in danger of that. i think it sounds like you're doing a great job. if you ever have any questions, please email me. i'd love to help!
good luck and cherish your little ones right now. as hard as it is, i promise you'll miss it! emma kate is already 10 months old and it has gone by TOO fast! :)
God bless!
S.