(((hugs))) to both of you, poor little guy.
Food allergies and insensitivities can absolutely present themselves through digestive issues and stomach pains, which in turn can disturb sleep. That's how it is for my younger daughter. She gets loose, mucousy stools, and with her milk allergy would also have blood in her stool from her intestines bleeding and disrupts her sleep.
It sounds like there's a chance he has some digestive issues going on - whether it is specific to a food or just in general is where it gets kind of tough. What is in the bread (i.e., is there soy? corn? anything that he hasn't had before other than wheat? same with the rice cake, I would take a look at all the ingredients).
What you can do is go back to his "safe" foods, his baseline, and then slowly introduce again. 1 food a week. It's a pain, I know, but if there are digestive issues/digestive allergy symptoms, it can take several days before they present themselves. Likewise it can take several days for the offending protein to get out of their systems.
Also - you may just want to ask to see a ped allergist and get some basic testing done (RAST blood testing, skin-prick, or skin patch testing - the allergist will determine which is best, probably skin patch testing which is what we do).
It could also be just a cold, or any number of things. It's hard to tell which can be very frustrating. What stands out to me again are issues after wheat and rice.
HTH and wasn't too confusing!
