What does the OB/GYN do?

I think they check the area in between your legs. my mom wants me to go.she just found out that my period has been irregular for over a year. im in 8th grade so I didnt think it mattered. I just skipped like 5-6 months and she freaked out. I cant take off my underwear for a doctor. I have lot of bruises on my inner thighs and I dont want my parents to find out. im still a virgin and everything its just this guy accidently hurt me a bit bad. when we shared a sleeping bag at a party that my parents dont knwo guys spent the nght at.it was an accident though. also if they really do check in between yuor legs then will they even ask me what happened. this is so scary. my friend told me that since I have one long cut on my inner thighs and big brusies they will ask me questions! help! im a really bad liar and I dont want to get in any trouble.my doctor knows me well and she can tell if I lie to her and she says that anything I tell her is confidential but I dont believe her. and if they dont check between yuor legs what do they check because thats the only thing that makes sense because thers nothing else wrong with me and I think my mom might be catching on to me about hiding stuff that I do with guys.