My son, Ben is exactly the same age and I am too suffering from sleep deprivation, I honestly think it's nightmares. He crys in his sleep and then wakes up startled. I had to really start paying attention to what was on the TV. Maybe your little guy is seeing something on TV or hearing something in books with his older brothers that is bothering him........I doubt on number three your letting him sleep too long during the day but every child is different.......The reason I think it's nightmares is that was the problem for my guy. We were watching Toy Story 2 and Woody had a nightmare......I knew it was frightening him and I held him tight and explained everything about it........when Woody woke up.......Ben had this look of understanding that was just too understood...and that is when I knew. We have been sleeping much better since he figured the meaning of a bad dream.
I hope this helps in some way, good luck with your little guy.