Prostatitis or something else?

[dannyd316]

I'm a 28 y.o healthy male. I've been having this problem for the last 2 months and nothing seems to help. I had unprotected sex with my girlfriend. We were both STD free but she did have problems with yeast infections in the past. During foreplay she squeezed my penis really hard a couple times. About 5 days later I began feeling burning during urination and 2 days later the burning in my urethra became constant. I also began feeling pain in my rectum (like a fullness in the rectum). Went to Dr. got tested for STD. Both our tests came back negative. I was given treatment for chlamydia/gonorrhea. Stopped having sex. Symptoms went away about  4 days after treatment but 4 days later returned along with lower abdominal pain and bloating which have continued since. Went back to dr. got another treatment (single dose azithromycin and suprax) but symptoms continued. Went back again and got transrectal ultrasound of prostate done along with abdominal ultrasound and more urine tests. All came back negative. Dr. says he doesn't know what it is so he put me on 10 days of doxycycline. Again, didn't work. Another symptom I have is lack of erections in the morning and I only get erections when stimulated and they go away pretty quickly. Also when I don't have an erection and I squeeze my penis there seems to be a pain in the urethra.
So now, could this be a yeast infection inside the urethra or prostate? or could it be urethra irritation or stricture? Or something else? Please help, this is driving me insane! Could it all be in my head?