I would take the antibiotics. Toby deals with similar issues with his epididymis, for him it is a chronic condition. When he first went to the Dr for it, he had to take antibiotics for about 3 months, and it is a particular antibiotic that is able to have an affect on that area of the body.
It is a good place to start, as making sure you are not fighting an infection, can help with further diagnosis. Also, it will actually help reduce inflammation there.
Get yourself checked out, you will probably be advised to change up your under clothing choices, they will want to check your prostate, and probably ask for blood work for PSA after the ultra sound.
Changing just how you sit on the bike should help as well. For heavy folks like us, we need to sit up and get off of our pelvic bones etc. Trust me, this is even a problem for a girl that has a plump rear and heavy thighs.
Wear the type of briefs that will pick your boys up a bit so you don't sit on them
I will be sending positive thoughts your way, I hope it is something simple and easily dealt with.