UTI after having sex?

I just lost my virginity last week to this guy I've been in love with for the past three years, we just made it official 6 months ago so we had sex for the first time... 
What I'm really curious about is this burning sensation during urination? It burned for about three days and stopped for a while, Then the burning sensation came back.
I sat on Web MD for a while, stressing out about everything I found and it basically said that it could be a UTI or a mistakened UTI that's actually an STI. And if it's an STI/STD I can't have kids or I'll basically have pregnancy problems. I'm seriously FREAKING OUT right now!!! I have no idea if it's a UTI or something more serious! Someone give me advice as soon as possible! I'm extremely confused and in great need of some reassurance.

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