My left thigh has felt numb for 1-2 weeks now and there is a lingering pain in the back of my leg what should I do?

Nerve. This suggests a pinched nerve as it enters the leg but also can be related to impingement of a nerve root up in the spinal area by a bulging or herniated disc. A neurologist is best qualified to evaluate and advise you. Imaging tests such as an mri of the spine or an EMG May be recommended for diagnosis.