Hello I Was Involved In Sexual Activity One Week Ago

hello i was involved in sexual activity one week ago my menstrual came this following on a Saturday on the Sunday i notice fine rash on my clitoral hood and when i showered i had a burning to the outside of my vaginal lip where it seems to be a bruised these weren't as before within the week after sex however. The rashes doesn't itch and the bruise only burns after washing when irritated, i don't have a burning sensation after urinating and there was no abnormal discharged. i had on a mess underwear and a very tight jeans for a whole day Friday before noticing the symptoms.( still on menstrual cant see a doctor just yet) could it be any signs of STI or something else??? completely worried.