I feel chill in my back and my thighs?

Anything else. May be you are having chills (shivering) that is common in the beginning of an infection such as flu, tonsillitis, otitis, pneumonia. If you have no other symptoms except for unpleasant sensation of coldness in your back and thighs and if it's been going on for a while, maybe you need to be checked for anemia, thyroid dysfunction. Maybe a good warm bath and some rubbing will suffice!