With all std tests clear and 2wks doxycycline my testicles part left still painful with back pain. tip of penis also in pain. is it epidymititis?

Not epididymitis: Infectioius epididymitis almost always involves only one testicle, with marked swelling and tenderness. And the only STDs that cause it are gonorrhea and chlamydia, so your negative tests rule it out. Pain in both testicles without swelling, and/or pain referred to tip of penis usually means chronic pelvic pain syndrome, similar to non-bacterial prostatitis. Wikipedia has v/ good article on CPPS.