You can read through the piriformis article and see if this matches the symptoms that you are having.
Muscle tightness is a common cause for sciatic symptoms and numbness and tingling down the legs. Of course, low back injury and disc problems can also produce the same symptoms.
Either way, talk to your doctor about your symptoms...what makes it worse, what makes it better, what feelings you are having, how long it has been going on, etc. They will be able to determine what is going on and give you treatment recommendations.
Hope this helps - comment back with other questions