Discharge that you see from milking or squeezing your penis is not a symptom of an STD. It's normal to see a discharge if you milk it or squeeze it.
Stop doing that, and let your penis just be, and see if you see a discharge. Your penis is your friend - treat it kindly. Squeezing it and milking it like that is not kind to it.
You've had negative tests - I don't know what you tested for and at what times you tested - but remember that anxiety doesn't mean infection.