What Is The Lump And Mild Pain In My Testicle?

A few years back i was a stupid guy fond of bdsm(sex) and other bondage stuff. While watching a bdsm clip i thought i would do the same with myself and experience the feeling. This all happened in 2008 when i tried putting a rubber band on my testicle. While removing it from my testicle my hand slipped and the rubber band hit my right testicle. Serve pain followed by that...and the next day i found a small lump on my right testicle..it isn't stable on the same place, its not a very solid lump.. Sometimes its visible...sometimes its not. Sometimes it pains ...sometimes it doesn't.. it used to pain for a long time. i got myself checked by a doctor ..i had to go an ultrasound test twice and a blood test..but both were normal. He gave me a few medicines and i felt better after a few months. I am a married guy now...i no longer have a fetish for bdsm and other stupid stuff. But i still have a mild pain on my right testicle..that lump is still there..sometimes its visible sometimes its not..but i feel the pain sometimes...and my right testicle is very sensitive than the left one. it also looks a little big sometimes.. It doesn't pain while having sex or ejaculating. i am planning to visit the doctor again. Does an injury lead to testicle cancer ????? What could it be ???? PLEASE HELP.