Pinworms, please help!

Hi, so I'm a teenage girl and I have pinworms... a lot of them. The first time I noticed them after going to the toilet was about 3 months ago. I got some medication for them from the chemist and after a couple of days they seemed to have gone completely, and I wasn't worried at all. Yesterday, I noticed them, a lot of them, again after going to the toilet and was really shocked to say the least. So I'm taking medication again, I've also cleaned everything and my parents have too of course. I'm just convinced that they never went, that they've been breeding more and more this entire time and that really freaks me out. I know that pinworms are harmless except for the itching, but I'm so scared that they're going to migrate to my female parts and cause infections or something... I've been doing so much reading and have scared myself stupid, hearing stories of people that are stuck with them for years! Basically, I just wanted to hear thoughts about this, about what I could do to get rid of them quickly and any ways to stop them from getting into my female parts? I'm sorry if it seems like I'm overreacting, I've just always had a weak stomach to begin with :( any advice is really really appreciated, so much!