You have received great advice. It could be any one of the things mentioned by everyone here. Here's what I can add:
The same thing happened with my son around that age, he woke up screaming like never before. I was sure something was wrong. Eventually we figured out he was hungry. We just never thought that was it because he hadn't been waking at night since he was 11 weeks old. After that went on for 3-4 nights of night feedings we learned that his last bottle before bed had to be 2 oz bigger than his daytime bottles, and we added cereal. That night and every night after he slept through with no problem.
If your son is teething - I highly recommend Hyland's teething tablets, but don't by the Lil' Remedies brand teething tablets because they don't dissolve.
Whenever my son had an ear infection he would cry whenever he laid down (bed, changing table, etc) because the pressure in the ear changes when you lie down and it is more painful. Pay attention, if he is even whimpering more than normal during diaper changes, or whining when lying on the floor playing, it could be that. My son always ran a slight fever with the ear infection, but not too bad.