See a Doc. This is something that needs to be seen by the doctor who either put the cast on or ordered it for you. Sounds like you are getting some pressure on one of the nerves in your leg. This needs to be addressed right away. If necessary go to an er.
Get an eval. See your family md for evaluation. This has many possibilities and all of them deserve evaluation by a dr.
See your MD. These symptoms can be vascular or neurological. See your physician to figure out which and the best treatment.
Carpel tunnel. Carpal tunnel syndrome is one possibility. Usually the numbness is felt in the thumb, second, 'third and the inside of the fourth finger. In carpal tunnel the median nerve is squeezed and this causes the numbness. Other neurologic conditions can also cause numbness such as pinched nerves in the neck, shoulder, or along the arm. When you are evaluated, these are conditions that will be looked for.
Neuropathic. This could be nerve involvement due to a pinched nerve in your back- herniated disc possible. An exam is good place to start.
Nerve. This can be from nerve compression from a disk in the spine or arthritis. It can occur in patients with vascular disease of the leg. It can also occur with muscle spasms in the lower back causing associated tingling in the extremity. If it's bothersome enough, see your family md for eval.
Couple problems. May be seen with peripheral neuropathy or nerve compression, but could be associated with decrease in blood flow. If associated with pain, numbness or weakness, see your doctor soon.
Leg tingling. Leg tingling = paresthesia of lower extremity.