Your doctor has, no doubt, delivered hundreds if not thousands of babies. He or she has seen the vagina stretched wide open to allow a baby to come out. He or she has seen the placenta delivered. He or she has likely seen every STI imaginable, including ones not so visually appealling like herpes or warts and had to remove them chemically or surgically.
Hemorrhoids during pregnancy are pretty common, like many other posters have mentioned. You won't be the first and certainly not the last patient to present with one. Just say "I'm not sure, but I think I might have a hemorrhoid. My symptoms are ____" and that's it. He or she will be able to help you.