Why does the back of my leg muscle ache when i walk up to my buttock like a shooting pain?

Leg pain.: Shooting pain from buttocks to legs could be a result of sciatica. By definition, a sciatica nerve that is located between the buttock muscles is being irritated or pressurized to cause sciatic pain. This particular pain symptom occurred typically in obese person and athletes. Resting and avoid strenuous physical activities can alleviate the symptom. OTC topical pain cream/ointment can be useful.

Sciatica: Pain in the distribution as you suggested describes the pattern of the nerve that travels in the leg called the sciatic nerve. The sciatic nerve is not the cause of the pain source, it is the result of an irritated nerve typically in the lumbar spine (low back) which are caused by herniated disks, spinal stenosis or degenerative disc disease requiring further evaluation by a spine specialist.