M.M.
This is behavioral.
DH and I have been dealing with this with our (now 4.5 yr old) son for 2 yeras. We hit our breaking point earlier this year. He was getting up 1-4 times/night. Sometimes for a drink of water, sometimes screaming....bottom line...we'd go in and tuck him back in.
We took him to a sleep doctor, and a sleep therapist. Nothing physically wrong with him, so the therapist helped us totally rearrange his bedtime routine. I'm happy to say that we've have more "sleeping all the way through" nights since we've made changes than "wake up" nights.
Our changes:
-No sugar from dinner time on. He'll have some goldfish crackers and water as a pre-bed snack.
-No TV! After tub, it's straight to reading stories.
-Earlier bedtime. Was 8pm...now it's 7:15.
-Alarm clock that tells him when he can get up. You can get it on Amazon.
PM me if you'd like to talk more about this. I was skeptical and thought nothing would work. We'd tried everything. But totally overhauling his routine has made a huge difference in our sleep!