Knot on back side of testicles where vein is no pain when i touch or ejaculate but pain along the bikini line not a bad pain?

Don't know what you: Mean by "knot", or "bikini line". A painless mass in the scrotum or of the testicle should be evaluated by your doctor who may or may not recommend an ultrasound of the scrotum. Try that route.

Go in.: Go in and see your physician for an appropriate physical exam and work up. It could be an std or infection or viral. Have it checked.