Went to GP with slight tingling in left leg. He dismissed MS because I showed no other symptoms. Chalked it up as compressional neuropathy. Now my feet are burning, especially when I sit, they feel like they're on fire. Could that still be caused by compr

See neurologist. You might have bilateral tarsal tunnel syndrome if nerves are trapped at ankle, but far more likely is the presence of a peripheral neuropathy, which needs attention to uncover cause and control your symptoms.
Yes. It could be due to that, But it also could be due to diabetes, heavy metal poisoning and other nutritional deficiencies. I think you need to return or see another doctor for a complete workup including labs and possibly an imaging study on your back.