Crown put on over a year ago. I'm 7.5 months pregnant that tooth is getting sensitive and painful.

well during late months in pregnancy you may get an xray to r/o any infection.
it is possible following a crown placement the pulp gets too stressed and eventually will need a root canal. you need to see a dentist to figure it out

The first trimester is the most critical, so normally avoided (unless emergency/infection). 2nd trimester is ideal, and 3rd is more a comfort issue (fetus putting pressure on descending aorta, etc).First step is to be sure you had your teeth WELL cleaned at least once if not twice during pregnancy.  If your tooth STILL hurts, then the nerve of tooth may be issue.  Leaving it alone is worse for the baby than having treatment, so go see your dentist.