I went to the er yesterday with extremely swollen testicles with no pain. was given a broad spectrum of antibiotics while there. swelling went down a lot throughout the day today, but it started swelling again badly. when should i go back?

Swelling of the testicle can be the result of poor drainage of fluid in the body. I am not sure if you were given antibiotics to take at home. So, my question is can this be an infection that needs more antibiotics- infections can also cause testicle swelling. In the end, I cannot address your concern without more information, You should see a doctor in person

Painless swelling of the testicles is not common. I would guess that is was scrotal swelling, although without more information it is not possible to know for sure. Make an appointment with a urologist for proper diagnosis and treatment.