Hi Jewls1962 and welcome to the forum.
Have you ever tried Dr. Scholl's Custom Fit Orthotic Inserts?
They have this computerized footmap analyzer that evaluates your foot length,arch type and pressure points, so you can get the best inserts for support & comfort. And the price is reasonable, but you have to keep in mind that you probably need shoes about half size larger.
As far as what could be medically wrong, one area to look into is spinal issues that would affect the feet,like spinal stenosis at L5,S1.
Plantar Fasciitis is another possibility, which I would assume your podiatrist ruled out, as most of the time just the patient's history and a clinical examination is all that's needed for PF diagnosis.
PF -along with many other fibro symptoms- could also be linked with sub-clinical low thyroid function or thyroid resistance, not usually detected by standard serum thyroid tests.
A chiropractor might be also another health professional, who would be able to determine if an adjustment of some sort might help correct some postural defect, that puts extra pressure on your left side.
Hope this helps, however it's not intended to replace medical advice.