Sex is very painful, mostly at the beginning. Causes? Does anyone else have this problem?

I am 20, and me and my boyfriend have been having sexual problems lately. Sex is very painful for me. Usually it gets a lot better about half way through, when i get wet, but before that, it basically feels like when you repeatedly bang into a sunburn, which lol i know isnt possible, but it hurts alot and that is the only way i can think of discribing it.

We dont have problems with other things, only this. I find him sexy, he turns me on, i turn him on, but for some reason, even if i am very turned one, i still cant really get wet enough to make it hurt less. So the amount of foreplay doesnt seem to help me. Ive watched porn together, given each other oral sex, and done many things to get myself going, but nothing works. And even when i am wet, some areas/positions still hurt.

Sometimes, after sex, i feel like i cant empty my bladder enough, i know that is a symtom of a uti? Is that something i could have? I also sometimes get white discharge and itching, but some seem to say that is normal? Yeast infection? I tend to overreact my symptoms and usually it is nothing, but do you think i should get it checked out?

Could i have an std? Hiv?

Dyhedration? Does that have an effect?

or is it normal for sex to hurt?

Sorry about how unorganized this is. I am just trying to remember everything i wanted to say.

Thanks in advance to anyone who takes the time to comment.