Discharge from the penis and sore/ cramped stomach

I believe that these syptom started the day after having sex unprotected with my girlfriend.... I noticed it because I like to wear powder to stay dry and every time I went to the bathroom I notice the powder caked up around the head of my penis... This have never happen before and I've been doing this for over a decade... My girlfriend said she have'nt sleeped with nobody else and she haven't had any unusual syptoms latly but, her body has been going through some unusual changes n the last year... Her vagina doesn't smell the same and during sex for over a year there has been a white substance like yeast or something that comes out everytime we have sex... She has been to the doctor for a STD screening and everything is negative including HIV, no yeast infection or bacteria... Could you please help me understand what could be going on because I'm thinking that she sleep with someone and contracted a STD or what ever has been affecting her body is now affecting mine, and if thats the case why all of a sudden NOW???!!