what is this ?

ok on friday i had sex, woke up sunday and it burned to pee, not like a uti, it feels just like a cold sore in your mouth, i just got tested a month ago, and my test cane back negitive for everything, im young, so it scares me not knowing what this is, i think i just rubbed my skin raw, but idk, someone please put their opinion in on this. ( when i say it burns when i pee, it burns like putting alcohol in a cut or sum, like putting salt on a cold sore in your mouth.