What could be the reasoning to having sharp pain and slightly swollen right testicle and lower sperm volume? ive had this going for the past week, age 20, no medications, no drugs, got a test for stds and the rest and all is clean?

I assume there has been no trauma. You're describing inflammation of the testicle ( orchitis) caused by bacterial or viral infection. Sometimes the cause is unknown. Epididymitis may be associated. Mumps is the usual viral cause. You should see a urologist ASAP for appropriate testing,accurate diagnosis, proper treatment and follow-up.

Low volume semen is not a result of testicular pain. . Wear a support underwear, use la heating pad and use Ibuprofen for a few days. If not better pl see a Urologist - you might have Epididymitis