I am 33 and i have a pain behind my knee whenever i kneel down or bend by knee more than 90 degrees and push knee out. ?

Need to be seen: It seems that the issue is on the front side of the knee . When you exert as you describe , you are applying pressure on the anterior knee structures . The knee is complex structure , with joint , cruciate ligament , anterior and posterior collateral ligaments , the patellar tendon etc. You need to see your doc to have physical and some imaging studies

Baker cyst?: You may need MRI of this knee. Chances are you developed baker cyst. Tx for this condition is usually conservative unless it broke; it it broke than you may need surgery. Mri may also shed light on other conditions. Go and see your doctor to sort it out.