D.W.
Babies do change their sleep habits a lot, and very unexpectedly. There's definitely a reason he's waking up. It can't hurt to offer some milk to see if he's hungry or to perhaps give an extra feeding before he falls asleep.
It could also be that he has something else going on that is making sleeping difficult. Have you taken him to the pediatrician to check his ears or to see if perhaps there's some acid reflux? It could be lots of things.
My kids are completely different sleepers - one good, one awful. They're just different kids.
I hope you get it figured out soon.
Best wishes.