Mystery STD

Patient: I am a 21 year old male who had unprotected sex with a female. Shortly after the intercourse i started to feel not 100. After that i started to develop a rash that then spread to my scrotum groin and anus. I also developed a rash on my arms. My stools started to change. They turned to a light brown yellow with a mucus like look to it. Also my tongue and throat have started to feel inflamed with white areas. I have seen my doctor but he doesn’t know what to make of it so he prescribed me doxycycline. What could this condition be?