R.S.
Some babies are not yet ready to sleep through the night, so this may be normal. Why do you feel you need to go in there every time? He may be wet, but not uncomfortably so. And a 1 1/2 year old boy never needs to feed at night. He may be getting up because he is expecting some sort of social interaction with you. On the other hand, he may really need his diaper changed or he is too cold or hot, whatever. What I do is wait about 5 minutes or so before going in to see what is wrong, unless he is crying hysterically from the start. If he still fusses, then I go in, address the need (I don't feed him), and quickly rock him back to sleep. I bring him into my bed if I sense that something is really upsetting him, and, after he is asleep, I bring him back. Works for me. Good luck.