I Stupidly Had Unprotected Sex 3 Days Ago. Today It

I stupidly had unprotected sex 3 days ago. Today it burns when I pee and I constantly feel,like i have to pee. Since I was on my period and I coulnd remember taking out my tampon I thought it was that but after feeling around I don't feel the tampon so I must have taken it out...I think it's a uti but I'm not sure