Its unlikely this increased sensitivity in the testicles is STD related.
More likely its anxiety.
No discharge, but I taken a short course of antibiotics...still sensitive in the lower testicals, via the sperm tubes..
If you only received masturbation (as in, only with hands), then its unlikely you had exposure to an STD.
Was there oral contact, or exchange of fluids?
Did the person who gave you masturbation had some kind of sores on their palms or whatever?
You mention 'know discharge'... please clarify is 'know' was meant to be 'no' or 'known'... or better yet, is there a discharge or not?
Finally, I will repeat this again: if your encounter was purely masturbation and there was no oral, etc... the possibility of contracting an STD like that is extremely unlikely (next to impossible).