I work out regularly. recently i developed pain under my hip on the left side. the pain than spreds to my knee. the pain is not constant.

Possible sciatica: Your description of your pain sounds like you might be experiencing inflammation of your sciatic nerve. Start with stretching of your lower back and hamstrings, with oral nsaid's. If that does not help, see your doctor.

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.