Ongoing Testicle Problem.

Hello, Back in 2004 I noticed having a discharge/itch from my penis after having sex one day with my (ex)girlfriend (Noticed the symptoms about 2 weeks later). We've had sex before for 2 years prior without any problems. Anyway... I went to the Dr. He prescribed me with 2 weeks worth of Doxycycline(was diagnosed with NSU). After treatment all is good for about 6 months or so ... same thing happens again, except I development an ache in my testicles. My Dr. sent me to a urologist. He stated that I had Epidermiytis. Prescribed me 2 weeks of Doxycycline again. All is fine for about 8 months. Now the most recent occurance happened in Late August of this year. I had unprotected sex with a women, symptoms started again (buring when I pee, no discharge this time, have an ache in my right testicle with minor cord swelling, lower abdomen pain/back pain.) went to the Drs again,(Tested negative for everything) just figured it flared back up, whatever it is. Though Doxycycline didn't help at all this time. I have no idea where to go from here. I did see a diffrent Dr this time around... he said that it could be due to drinking too much caffeine.

Here's what I tried so far:
I went as long as 1 week without any caffeine(that may have helped a little bit)
No masturbation for 5 days (No help)

Should I cut out mastubation and caffeine completely for awhile to see if thats the problem?

keep in mind:
I never tested positive for having STD's.
Doxycycline sometimes helps though.
Somehow I've been dianosed with both NSU and Eyperdermitis(or whatever that's called lol)
The ache is usually always only in my Right testicle/lower back, as well as the swelling of the cords connected to it(testicle).

Right now I feel a burning sensation in my Urethra (during urination and not) a slight ache in my right testicle, and lower right side of my back.

I have no idea what to do?

Suggestions?