The transient discharge likely was nongonococcal urethritis (NGU), which probably is someimes acquired by oral sex - probably caused by bacteria that are normal in the mouth but cause problems in the urethra. So it's no surprise the standard STD tests were negative. The azithromycin (Zithrommax) probably cleared it up.
However, the penile rash/peeling doesn't sound like any STD. I can't judge whether lotrimin helps because of its active ingredient (an anti fungal medication) or because it just moisturizes the affected area. But if it's a fungal infection, the hydrocortisone won't help and likely would make things worse.
Bottom line: the itching/peeling problem isn't an STD and almost certainly is coincidental with the sexual event you describe, not caused by it. Consider seeing a dermatologist; don't use any treatment of any kind in the 10 days before your appointment. In the meantime, you can be confident you don't have anything you can transmit to a sex partner.
Good luck-- HHH, MD