Pain in back can be due to several reasons. One of which can be pelvic causes like ovarian cyst
which cause pain only if its huge enough to cause dragging sensation or due to stretching. Besides infection , rupture, torsion of cyst can also cause pain but that a very sever pain associated with vomitting and fever in infection. To get a picture you should get an ultrasound
of abdomen and meet up gynecolgist personally for a complete pelvic examination.
As you said your backache
radiates to leg and more towards left side, it can also be due to some kidney
cause like stones. An ultrasound will help you to know that also.
Besides due to abnormal postures at work, sometimes spinal nerves get pulled or compressed which can also cause pain.
For now you start taking analgesics like brufen
and meet your gynecologist soon.