I disagree with the tactic of letting them cry it out.
I'm sorry, but I am the kind that wants to make sure they know I am there. Kids cry for a reason, and wanting to feel you close is a good one.
when my kids cried, I held them close to my heart.. and just made shhhh shh sounds.. or sang a very low tone song.. something that can calm them..
Notice doing something different every night, and see what works.. but sometimes it's just that they miss having mommy near by.
Ifyou think it's the food, don't feed them acidic things at least 4 to 5 hours before bed time. and if you think it might be the gas, try not to give him milk, or dairy products before bedtime, etc. Try giving him water, and letting sit up most of the time.
When my kids cried.. Most of the times, ended up sleeping with me, and that was the best thing for me. As a mother, I felt good that they calmed down, and eventually they grow out of it.
Good luck, and do what your heart tells you,
C.