4.Swelling
Swelling can be a sign that you have a sexually-transmitted disease like gonorrhea as well. The swelling will usually only happen with guys because it almost never happens to any areas outside of the testicles. However, it can be difficult to know if your testicles are swollen. If the swelling is only slight, then looking at them is not going to help, so you should pay attention to how you feel instead.
Most guys know what it feels like to get injured in that particular region and swelling of the testicles can have some of those same sensations – especially the ones that occur after the injury has occurred and after most of the pain has gone away. This will usually build up over a period of days or weeks, so you are going to have to pay attention after each sexual encounter.