Thanks for reading the forum for similar questions before asking your own.
First, your symptom of penile discharge during a bowel movement: this is a common symptom in many men, usually not a sign of anything abnormal unless it occurs frequently. It is due to the pressure of defecation squeezing the prostate gland, expressing normal fluids. Here is a thread from just a couple days ago that discusses it, which also has links to other treads:
http://www.medhelp.org/posts/STDs/1124068
Also, your negative tests after your exposure a year and a half ago show you were not infected; if you were, the antibiotic therapy should have cleared it up; and it is very unlikely any infection would persist for 18 months. To your specific questions:
1) You might have read Dr. Hook's and/or my previous comments out of context. Gonorrhea rarely persists more than several months. The longest chlamydia has ever been documented to persist was 4 years, in a single woman among several hundred studied. In 90%, the infection was gone within a year, without treatment. Persistent infection is believed to be even less common in males.
2) Frequent urination would not affect test reliability.
3) Urinalysis misses most STD. But as discussed above, all evidence proves you don't have a current STD (and probably you never did).
4) In the doses used for most infections, clarithromycin (Biaxin) would cure either chlamydia or gonorrhea.
See your primary health care provider if you remain concerned about any symptoms. But there is no basis for concern about any STD.
Regards-- HHH, MD