Sleep Regression? Teething? Missing Mommy?

So for the past couple weeks (I forget how long exactly) Little Man has been waking up several times a night. My son started sleeping through the night at 8 weeks old, so I’m a little curious about why he suddenly started waking so frequently. He will stand up in his crib and just start screaming. I will promptly come in, nurse him back to sleep, and he will sleep for another couple hours. Some nights he only wakes once, others he wakes multiple times a night. 
I guess the one thing that is bugging me is that I don’t know why exactly he’s waking up. But I guess that’s a lot of parenting…you don’t know the why’s. You just need to be there and help them get through whatever they’re going through! I think I, like so many other mothers, sometimes get caught up in selfishness and say, “Why can’t he just go back to sleep?” Those are growing moments for me, where I sort of step outside myself and see the world for my son’s perspective. I am his whole world (Daddy included), and if I were to ignore his needs, no one else would meet them! So whenever I get a negative, self-centered thought in my head I try to imagine my life without my son and how devastated I would feel without him. It might sound a little drastic, but that’s my thought process. I’m trying to enjoy each day with him because there will come a time when I’ll wish I could go back to this time via a time-travelling DeLorean and hold him once more as a baby.