Yes I would do you want to make sure the placenta is still intact

I'd go just because I'm expecting

Better safe than sorry is my personal policy.

Baby should be okay, did you hit your head really hard? I'd watch for swelling, if you start to feel dizzy/lightheaded/generally different than usual stuff (concussion watch basically) I'd go in.
Same with the butt minus the concussion part, if the pain gets steadily worse, you do have bleeding, etc I'd go in.