Welcome to the STD forum.
It sounds like you have a mildly symptomatic case of urethritis, i.e. infection/inflammation in the urine passage. The discharge is the main clue, but itchiness in the urethral opening and occasional pain when urinating also go along with this. My guess is that if you examine yourself closely when you first awake in the morning, i.e. when you haven't urinated for a few hours, you will be able to squeeze a little mucus-like discharge from your penis.
The most common cause is nongonocccal urethritis (NGU), a catch-all for several possible causes, including chlamydia. Gonorrhea is less likely, because the symptoms usually are more severe.
However, there is one big atypical feature here -- the delayed onset of symptoms. NGU, chlamydia, etc usually cause symptoms within 2 weeks of sexual exposure, but it sounds like your symptoms were delayed as much as 2 months since last sex. This raises other possibilities, such as non-sexually acquried urinary tract infection. UTIs are uncommon in healthy young men, but still can happen. They increase in frequency beyond age 35 and especially after age 40-45.
You need to see a health care provider to sort this out. Please do so promptly. Even though your symptoms are fairly mild, serious problems should crop up if it isn't properly diagnosed and treated. Please see your primary health care provider as soon as you can get an appointment. And it would be a good idea for your sex partner to see her provider (or go together to the same clinic or doctor) for routine STD testing.
Let me know how this turns out. Best wishes--
HHH, MD
Try to avoid urinating for several hours before you are examined, ideally early in the day before urinating (you can hold off on fluids the previous evening to help you hold your urine). Diagnosis is easier and more reliable when there is visible discharge, without having to rely on urine testing etc.