If you had a discharge from some type of infection, you would not need to squeeze it. Of course if you squeeze, something will come out. A discharge would consist of stains on the underwear and continuous "leaking" feeling.
Your test was conclusive and you have no worries about discharge from a STD.
This may not be an STD, usually whitish, greenish or yellowish discharge. I dont recccomend this but if you suspect STD, squeeze head of penis to see if any discharge comes out of it. dont squeeze after urinating or if you have to urinate. wait until your bladder is empty wait a hour or so and lightly squeeze head of penis, if discharge comes out, go to your local free std clinic and get checked out. BTW, just becasue you have discharge doesnt mean its automatically std. hope this helps. GL