5 Days back I had an unprotected sex with a girl in spa. It lasted for 10 sec and I ejaculated inside her. Her vagina was very dry. I asked her if she has HIV she said no she has taken some injection. Since yesterday I am feeling some sensation in my penis. However there is no discharge no swelling no lump no numbness nothing. It is just I feel something which I cannot explain. It may because of anxiety that I may catch STD. This was my first experience without protection. I am mentally disturbed please help what should I do.