Hi friend!
I just wanted to let you know that you shouldn't let anyone make you feel bad or guilty for considering formula instead of breastmilk for your baby! While breastmilk IS the best for your baby until they are at least 6-months-old, there is nothing wrong with formula... babies do JUST FINE on formula, especially if it's the right one for their little tummies. Your son will be better off and more happy if his tummy is not hurting him, whether that's on breastmilk with a restricted diet or formula that his tummy can digest better.
If you're able to find out what is irritating his little system, it sounds like you personally would be more happy with that option... to keep nursing as long as possible. BUT, if he continues to be uncomfortable after nursing, then there is absolutely NOTHING wrong with switching to, or at least supplementing with some formula!
I actually went through the same exact thing with my little one. Emma is now 2-and-a-half, and she is so super smart! :) The formula did not hurt her one bit! :)
We used Similac Alimentum (http://similac.com/baby-formula/similac-alimentum-hypoall...) and it worked wonders for her little tummy. While breastmilk is the easiest for normal tummies to digest, if there is a protein in the breastmilk that is causing an allergic reaction, it means that the baby's tummy cannot digest that specific protein... which causes the pain and gas. So, the formulas that are created for protein allergies have the proteins already broken down, so that their little tummies don't have to do the work. :) And then everyone is happy. Another brand, but the same thing, is Engamil Nutramigen (http://www.enfamil.com/app/iwp/enfamil/productDetail.do?d....
You might be able to get samples of either or both from your pediatrician... ours just supplied us with free samples, because it was so expensive. My mother-in-law also was able to find a supplier through ebay, believe it or not. She was able to get cases of it (all wrapped and closed and everything... brand new cases) for several dollars less per can. That helped a lot too!
Anyway, I hope some of this helps. I know how you're feeling. Emma was 4-months-old when we had to switch her to formula. I still nursed in the morning and when I got home from work, but the formula really helped her get what she needed, and calmed her tummy down so it was able to handle my milk the few times I got to nurse. I struggled with some guilt because I wanted to nurse until she was a year old, but honestly, it was better for both of us, because it was worse when Emma would scream and push away from me everytime I tried to nurse!
AND... her milk protein allergy went away by the time she was a year old, so she can drink cow's milk without a problem. :)
I know you've gotten a lot of advice. I just wanted to offer some support, and hopefully let you know that other moms have been there and its ok. Formula does not make you a "bad" mom. :) And, while breastmilk is ultimately the best for babies, sometimes they need something different, and formulas really are made very well now, and can be just what a baby needs.
Good luck! I'll be praying for you and your little guy!
Blessings,
S.