Brief Answer:
Read below.

Detailed Answer:
I read your question carefully and I understand your concern.

I am not sure who was that said it was sciatica but it doesn't look like that to me, at least not as the first hypothesis, it would be an atypical presentation. In sciatica symptoms usually are only on the one side and there is pain which starts from the lower back radiating into the limb.

Judging from that description of numbness and painful sensations in the bottom of your feet I would say that the most probable cause would be a peripheral neuropathy, damage to the peripheral nerves.

Such damage may be due to many causes such as diabetes, alcohol, nutritional deficiencies, certain medications or toxins, liver or kidney disease, hormonal imbalance etc, the list can be very long and at times no cause can be identified. In your case there is already one hypothesis, since you mention to have started metformin I suppose that was started for diabetes. Diabetes is by far the most common cause of peripheral neuropathy.

So what I would suggest is check with your primary physician or even better a neurologists for other signs of peripheral neuropathy such as altered reflexes and sensation. If the suspicion is confirmed nerve conduction studies and some blood tests are the next step. Routine blood studies include blood count, glucose, HbA1c, liver and kidney function, electrolyte panel, thyroid function, vitamin B12 level. Only when no other causes are found are tests for rarer causes ordered, if there is confirmed neuropathy on conduction studies and a history of diabetes I would say no more tests are needed.

If diagnosis is confirmed, management consists in controlling the cause as well as medication for neuropathic pain. Most common options for neuropathic pain are anticonvulsants like gabapentin, pregabalin or antidepressants like duloxetine.

I remain at your disposal for other questions.

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