Muy left leg has had a burning sensation for about a week now, from top right to my toes and it seems to be getting stronger, what could be cause?

Lumbar spine. Burning pain which radiates down the leg to the toes is commonly due to irritation of the lumbar nerves as they exit the spine. This could be due to a bulging or ruptured disc or just local muscle spasm. Check with your pcp for a referral to an orthopedist or spine specialist. You will likely need lumbar x-rays and possibly an MRI if it persists.
A nerve impingement. In your lower back possibly.
Burning. Sensations like burning and tingling can be a sign of undiagnosed diabetes or another nerve damaging condition. If you haven't been thoroughly evaluated by your podiatrist or neurologist, you should schedule an appointment right away.