Numbness in left foot

I have a laminectomy at L4 L5, 14 weeks ago for stenosis, and sciatica on my right side.  The results have been excellent, but with just lots of strange muscle aches and pains during the healing process,which I was told to expect.  My low back continues being achy when I sit for extended periods without break, which is demanded of me at my job.  This week, the sitting was more demanding than usual, and now my left leg and foot are numb below my calf.  I am terrified that the stenosis will return in my back, and hope this is just a posture problem and caused by the excessive sitting.  I'm unsure how to treat it, and have been taking Relafen and Advil.  Getting up and being active seems to relieve it, but upon sitting again the tingling starts up again.  I tried icing my lower back this morning.  It has continued for several days now, and I am getting more concerned.  Any suggestions for treatment?