Hey! I also breastfeed. I commend you for choosing to do this for your son!! My little girl is 5 months old now. She has ALWAYS had a lot of gas throughout the day - she even sometimes passes gas in her sleep at night. It can be really loud & smelly too, just like an adult, but she never really cries much with her gas so I guess that's the important thing. Babies have gas - but it's when they cry with their gas that you have to start really paying attention.
I've noticed that when I eat certain things she has more gas than usual so I try to limit my intake of spicy or heavily seasoned things. Chinese food & chocolate gives her more gas. But SHE HAS GAS NO MATTER WHAT I EAT. I think you're doing a great job watching your diet and that's about all you can do.
Something I've done to help my baby is to take her to the CHIROPRACTOR & the doc. said he could tell she was having some trouble in her intestines - after her adjustment I could tell this helped her with the gas & bowel movements. Also something else I've done is given her MYLICON DROPS or Little Tummies GRIPE WATER, it's natural.
*** And just remember, this too shall "pass" -- ha! :)