My 9 month old is constantly waking up at night crying in pain. i know he's teething, but could it be from switching from rice to oatmeal cereal?

Probably not teeth: It is unusual for teething to cause enough discomfort to awaken a child from sleep, unlike ear infections. His crying at night could be due to some separation fears which often arise at this age. I doubt the cereal change is causing pain unless there is significant constipation. Try soothing him with a transition object like a blanket at bedtime and it may help during the night.

Could be.: If going from a softer, less seasoned rice to a harder more seasoned oatmeal that is harder, that may cause more discomfort. Let the baby suck on an orthodontic condoned cold pacifier and relax the child with soothing baby music toys. The child needs to sleep sometime and if you cannot get the baby to sleep, see your pediatrician.

Maybe: If you do anything to treat or soothe the teething does the crying go away? If so, then it is just the teething.