Really uncomfortable ache on back of testicle and stomach after sex and cycling. Seems muscular, no sti. Had ages. What kinda doctor do need to see?

Start with regularMD. Get a good exam, may need tests like sonogram (sound wave pictures) of the area to check for varicose vein, cyst, fluid collection, mass, etc. May need to see urologist (surgical specialist re: genitourinary system). May be a hernia, would need to see a surgeon. First get examined.