7 months ago had unprotected sex with female. had lots of sti tests over 6 months including trichomoniasis, mycoplasma and ureaplasma. all negative. had sticky semen type discharge today when having a big poo (and once before). is it normal? related?

It is difficult to determine the exact cause of the sticky semen type discharge. However, it is not necessarily uncommon for men to experience occasional changes in their semen consistency or color, and it may not necessarily be related to an STI. Many factors can impact the texture and appearance of semen, including frequency of ejaculation, diet, hydration + age, certain meds or health issues.

Sometimes a bowel movement puts enough pressure on the prostate gland and seminal vesicles to squeeze out semen or prostate fluid. Your description is exactly right for this event. It is not an STD symptom and has nothing to do with the sexual exposure described. Nothing to worry about.