As the others have stated could be arthritis, but my instincts tell me its sciatica, by stating that it is stabbing. The sciatic nerve runs from your lower back and extends to your pelvis, thigh, knee,calf,ankle, foot, and toes. Therefore it can effect each of those body parts. It could very easily be a slipped disc, with the pain radiating to the hip.
My recommendations is to see a physician, specifically a chiropractor, insist on an exray, they have many new diagnostic procedures, to help you figure out whats going on. They cannot prescribe pain killers, but do usually suggest life style changes.
Magnesium is very healing to the body, will also help the muscles to relax,as is zinc. Vitamin B complex,will also help.
As far as shoes go, a good supportive shoe. That supports the arch, a one inch heal, with a back. No flip flops, or slides, and yes flats do make it worse.
If you carry a heavy purse, ditch it, pair down what you carry, always a contributing factor in backache, and sciatica.