Tingling/Numbness in Left Leg

Off and on for about 4 months now, I've been getting pins and needles all day long down my left leg, although it is most prominent when seated. Sometimes there is even a bit of numbness to the degree I can't feel my baby toe.

I have had an x-ray done on in my lower back/thigh area and nothing turned up. I went to a physiotherapist for a series of appointments which seemed to make it go away for a couple weeks, or maybe that was a coincidence.

My doctor still insists that it is related to how I am seated while I'm at my desk at work, but I already had an ergonomic assessment when the problem originally started happening and while it doesn't seem as severe it is still there so I have my doubts.

Should I attempt to get a second opinion on this or should I just try to change my posture/seating again?