What Causes Yellowish Discharge From The Penis?

ok last saturday 3rd of july i had sex with my gf wearing a condom. evrything was fine till the next morning i saw stain spots on my boxers, i pulled on my penis n a yellow drop of fluid came out (no it was not urine). since then i have been worried because i have read it takes 2-3 days for symptoms to surface, is this correct? i have no pain when urinating, just discharge, and it seems to be more yellow when i wake up n get out of bed in the morning. this is the 3rd day. discharge is stil there but there are no other symptoms.....what is the best course of action. get in touch with my local gp or go to a sex clinic