Problem: KT, a 20 year old college student presents to the student health center because he noticed a yellow green discharge from his penis the day before. He is sexually active and has more than 20 lifetime partners so far. His last sexual contact was 3 days ago. he does not know the status of his partner with respect to that partner's other partner. K.T. has no fever or chills; however, he reports burning with urination and purulent discharge from his urethra. What are the 3 possible differential diagnosis for this patient?