Seeing the lady doctor for the first time

I’m 20 and have been sexually active for about 5-6 months and have been with three people. I have never been to a gynaecologist before but thought it would be a good idea to see one, not because there’s a problem but because I think it could be beneficial.

I want to get a check up just to make sure that everything is okay but I do also want to make sure that I am clean, I believe I am but just want that assurance, but I don’t know what I’m supposed to ask for... and what usually happens when you see a gynaecologist?