blisters, soreness, and redness of the vagina.

So i had unprotected sex with a guy on thursday and by sunday my vagina became very sore and burned when ever i peed. at first i thought it was just a yeast infection ( i forgot to pee after i had sex )and so by monday i was back to masterbating ( even though it was still sore and irriated) only now i have found that my va jj has become sore to the touch and i have blisters around my vagina ( only like 3 ) but im still freaking out. could it be from the friction? or something else? someone please help.. im worried sick i might have an std