I just went through this with my 6 month old. He used to sleep really good, then when the teething began he started waking up every hour or two. Just like your baby, he's also just started rice cereal, so I wondered if that was the problem. I asked for help on this site and got a lot of good advice. What worked best for us was to feed him cereal at 8:30 or 9 at night (we started mixing the cereal with apple juice instead of formula and that was easier on his tummy). Right after he's done eating we give him mylicon to make sure he digests his food well, then it's straight to bath and into jammies and then we give him some infant motrin. This was the best advice I got from other moms on this site. If you're giving tylenol for the teething, this can have stimulating effect with some kids. So we switched to motrin cause it has ibuprofen instead of acetominophen(which is what tylenol has). So after a dose of motrin he goes straight into his bed and we let him cry it out after that. We just started this a couple days ago and the first night he woke up 3 times, crying for 15min each. Then last night he only cried 5 min each, so it seems to be working well. We did the crying it out thing with our first son too and it worked great! He only did it for 3 days and he's slept thru the night every since.
I really do feel your pain, as I said, we just did this for the second time literally days ago. It is so hard to let your kid cry it out, but believe me you'll be so glad you did it in the long run. Your baby is definitely old enough to not have to eat during the night anymore, just make sure he/she is nice and full when it's time for bed. We did this whole thing with our two year old and we're so glad we did!
--Like I said, the best thing for us was switching from tylenol to motrin!!!!!!
Good luck! This WILL end eventually just like all other phases!