you may have what known as a vericoseal. its a vien in the testicle that becomes large and enflamed by lack of support and heavy physical activity. looks like a lump on your balls.
i have one and i sometimes feel a dull ache if i ski or skateboard in boxers and not briefs. wear more supportive underwear and take some asprin.
it sounds like you may have something like this or worse. go see a doctor.
i thought i had cancer or something. buts its no big deal.