Girl talk and Advice!!

Karla
So I recently had sex with my boyfriend for the first time (I've had sex before but it was the first time with him) and he had joked around about this dick being big but I thought he was playing but turns out his really big, now I'm 18 years old, and the sex was good but still a little painful and didn't last long , any advice on how to handle the size? Also that's been 3 days ago and since then I've had this burning sensation when I pee and there's a little spotting and have urge of peeing but barely pee when I go. I think it might be uti, any antibiotics recommended? I really need some feedback, thanks