Pain during sex

Since I’ve become sexually active soon as it goes in it hurts soooo much, then once it finally goes in it literally feels like it’s burning and that’s all my mind can think of so my vagina walks start to clench up. I’ve read online I’ve never had sex with anyone else in the past so I can’t have an STI, I’m only 18 and iveused condoms I’m worried what to do or what it is