I sit down and straight my left leg and pushing my body forward and , i feel a pain in my left hips . doctors said it is not sciatica \ piriformis?

Sciatica: The piriformis muscle sits very close to the sciatic nerve and for some people it actually irritates that nerve and causes pain to radiate down one or both legs. It can be difficult to distinguish from a disk herniation which irritates low back nerve roots that also causes pain to radiate down the leg (sciatica). Piriformis syndrome can be treated with injections and / or pt.

Sacroiliac: Your pain may be in the si joint anti inflammatories and proper exercise are very important. Stretching out your hamstrings, glutes and quads also may help. If these fail to improve it you may want to get a second opinion.

Likely Low Grade: Sciatica or Sacroiliac Joint pain. Piriformis Syndrome is rare, however it can be a possible symptom as well. Generally internal rotation of your hip or actual pressure on the piriformis muscle will cause pain if you have piriformis syndrome. If no improvement in a few weeks, go back to doctor for further evaluation.