Around this age many babies have a growth spurt. You can start offering him more food during the day to help satisfy his hungry tummy later on. You could also put a sippy cup of water in his crib that he can find by himself during the night. You could use a bottle with water in it, but you might not want to head down that road.
Another reason is that the baby could be getting teeth or more teeth. Even if you can't see them, more teeth are pushing their way to the surface or cutting through the bone, which is actually more painful than cutting through the gum. The ones in the front are no biggie compared to the ones in the back. You can try leaving a cool chew toy in his crib for the night (or if you are using water in a bottle this will do), and you could also give him some Tylenol before bed and see if that helps him.
If it isn't either of these things, he may just be going through a "separation anxiety" stage. He may have not awakened much before in the middle of the night and realized you weren't there...and now maybe he is! If you really feel the need to check on him, resist the urge to pick him up if everything seems to be ok. Put on some soft music and sit with him for a few minutes and leave quietly.
I hope this helps.