Hi Mareea, unless you had real deep sex and your hyman was broken but thats still intact you should be OK, at 18 you should be with your doctor or your own, if not just ask your mother politly to see your doctor on your own, what happens between you and your doctor should stay that way.
Good Luck
Yes, the dr can tell if there was intercourse. If his penis was in your vagina, the dr will be able to tell. However, because you are 18, you have patient rights and under certain laws he cannot tell your mother that you have done so.....