Pain In The Lower Abdomen And Back Pain While Urination. Had Kidney Stones In The Past. Normal STD And Blood Test. Reason?

i frequently urinate and when i pass the urine there s this painfull pain on the left side below my belly and a back pain on the same left side which nnever gose away, and when i urine it increases with the sharp an painful one below my belly on the same side, i went to 2 different doctors, one side i had PID, the other side kidney stones , all the different medications never worked, i did x-rays altru sound, scan my whole body , all my organs, with a contrast, and dye, an still they all side the same thing, they dont kno what s wrong , because all my organs or fine, and i have no infection, i did STD S TEST, BLOOD TEST AIDS test everything keeps comig back normal, now the problem is, that when ever the pain eas down , it dont ever go away, it comes back with the same sharp and painful pain everytime i have a period, and stays for 2 to 3 weeks untill it comes to a mild pain and it stays till i have another cycle, which always comes and last the same 3 days every time, so can you tell me what my problem is, what my doctors or missing. plz..