Feels Sore And Itchy, Burning After Having Sex. Could This Be A Repeated Yeast Infection ?

Hello, I am a 15 year old girl (yes i know i am young) but i have been sexually active with my boyfriend for 9 months now. At the beginning of this, we used condoms and everything was ok. I felt a little sore afterwards but i'm pretty sure that was because we didn't do it very frequently. About 3 months ago, i started taking birth control and so we stopped using condoms. A month ago, i got a uti and a yeast infection which went away with some pills i was perscribed from a doctor. But now after having sex about an hour later i start feeling itchy, and it starts burning, i think i'm swelling but i haven't looked for any redness, and when i try to have sex for the second time in one night it kind of hurts and feels sore. I don't think its a yeast infection. And i don't think its an std because although my boyfriend has had other parners. I'm the only one he's been with in over 3 years and he was checked for std's and came out clean, and i have only been with him. I was wondering if this was maybe a semen allergy? Or what else could it be? And how can i get this treated? I don't have any way to pay this 15 dollars either. If you could just please send it to my email.