White/Yellow discharge after having Sex with partner and both test Negative for STD's ?

Hi, I have a long history of infections by having sex. I will give a layout of my sexual history since I started having sex. I had more sex in between with condoms where I did not have a condom breaking or slipping off, those I will skip as nothing happened.

I started having sex about 13 years ago. I was with my first girlfriend for about 1 year. Most of the time we had sex with a condom. But we had sex about 10 times without a condom. Everything went well and I never had problems.

About 4 years later I had sex with a girl. I noticed a white/yellow discharge from my penis with some itching after one week. I was tested for an STD and then it came back positive with Chlamydia. I then told the girl she should also get tested, she told me that her tests came back negative. Well I don't know if she told me the truth or not but we never had sex again.

Since I had Chlamydia I have been super alert about this and till date I monitor my penis regularly for any discharge or irregular discomfort.

A year later I had sex with another girl. I also got a white/yellow discharge from my penis within 3 to 5 days after having sex. I went for and STD check and all the results came back Negative. I got a 5 day course of Antibiotics and everything cleared up after a week. I never had sex with this girl again.

About 6 months later I met another girl and we went out for 4 years. When we had unprotected sex for the first time I also got a white/yellow discharge within about 3 to 5 days. I went for an STD check and I also told her to go for an STD check. Both of our results came back Negative. Both of us received a course of Antibiotics. My symptoms cleared up and we had sex several times thereafter. During the course of this relationship I would sometimes get an itchy feeling in my urethra and sometimes in the morning before I urinate when I squeeze my penis a little bit of white discharge will come out. It was not to alarming for me as I knew both of us was clean when we did the STD test and it was Negative.

About 1 month later when I broke up with the previous girl I had sex with another girl. I got the same symptoms of white/yellow discharge again within 3 to 5 days. I went to the doctor and STD test. Everything was Negative again. The doctor gave me Antibiotics and everything cleared up. I never had sex with this girl again.

About 1 year later I had sex with another girl. Well same symptoms white/yellow discharge within 3 to 5 days. Went to doctor and STD tests was Negative again. Doctor gave me Antibiotics and it cleared up again. I never had sex with this girl again.

About 1 year later I went out with a girl for about six months. We had sex the condom broke, my penis was in her for about 1 minute without the condom. Well what do you know within 3 to 5 days I had the white/yellow discharge. After being to the doctor so many times for this same problem I felt shy so decided to leave it. I did some research on the internet and found that they said Cranberry Juice and Garlic helps for Urinary tract infections. I started drinking high doses of garlic pills and it took the discharge away for a week or so and then it came back but not as bad. When I stopped drinking the Garlic it will get worse, but with the garlic the discharge almost disappears but comes back again when I stop drinking it. So after a month of struggling I decided to go back to the doctor. Had the STD tests done and nothing everything Negative.

So about 4 months later I was in a serious relationship again that lasted for about 4 months. I had sex with her and I got a white/yellow discharge again. It was not as bad as the others I have had as I kept on drinking the garlic to try and prevent any infection. So my doctor send me to a Urologist and he tested me for STD's. The results all came back Negative. I still had sex with this girl several times afterwards. I never got Antibiotics and after about a month the Discharge cleared by itself.

So about a month ago I went for a standard Cholesterol test and the doctor asked me if he can do a general STD test as I had these previous problems. So the tests all came back Negative for STD but I had blood in my urine. So I was send to the Urologist and he did a Cystoscopy to see what is wrong. He found a narrowing in my urethra so repaired this and everything else looked good. So now I have been walking with this catheter for almost 2 weeks. For the first week I received Antibiotics to prevent an infection, now after about 10 days I notice this same white/yellow discharge coming out of my penis next to the catheter. I will see the Urologist in 2 days when he has to take out the catheter and also ask him about the discharge.

Questions:

1. Is it possible for one person that tested Negative for Chlamydia or any other STD to infect another person with Chlamydia ?

2. Do I have some kind of an allergic reaction to a woman's vaginal fluids or what is causing this white/yellow discharge after I had sex with a new partner ?    

3. Can anyone explain why I have had the above symptoms as soon as I have unprotected sex ?

4. Any advice with regards to this will also be welcome ?