Red Rash Reoccuring On Penis

I have had quite a bit of problem over the past year with a reoccuring rash on my penis with the following symptoms:

painful in nuts quite often after ejaculation.

Red rash on penis head that seems to be brought on more by ejaculation then anything but when the rash is present it is sometimes sore to pee out of my urethera. I am using no new soaps or anything in the area.

Sometimes a couple times of ejaculating will cause my penis to feel like it is burning on the inside of it. It is like the muscle that releases the sperm gets sore and so do my balls.
Before october I had no trouble at all with any of this.

I noticed that it burned when I urinated back in october and went and got tested for std's. I also had a red rash around the outer rim of my penis head. It wasn't very big but is actuallys till there. It kind of goes away and comes back. They dismissed it and my tests came back negative.I got the bill for the first doctor and it was high as hell. So that stopped me from going back for awhile. I ended up going back and getting tested at the public health center and my tests came back negative as well.

The first doctor visit they gave me a shot.
The 2nd, I got some erthromyician andanother drug. My understanding is that I was treated for ngu and urethitis. Anyway... I am wondering where to go from here and can't really afford to throw alot more money away without some idea what is going on.

At one point I psyched myself out and psychosomatically shut down my sex drive for awhile because I was so worried about this. My drive is back but before it came back:

i went to the doctor and they did a testerone test and it came back normal. My drive isn't completely gone anymore because that part I think was psychosomatic and I was making it die. I do however have soreness in my balls on a regular basis and like stated before still a rash on the head of my penis. I don't understand what is going on. Do I need to go visit a urologist or what? I've gone to the doctor so many times and i'm getting really discouraged.

Update: went to a urologist and he didn't tell me anything. I got my prostate checked and it is
is fine.

What could this rash be becuase I believe it is the cause of all this. Should I go to a dermatologist now because thats what the doctor recommended.

I just feel like i'm getting the run around and nothing is getting accomplished and I keep having to do all these uncomfortable tests.