What could be causing my right thigh to be numb a lot? Also my shoulder and back of head fall asleep when I sit a certain way.

Numbness. This is most frequently a sign of pressure on the sensory nerve that anatomically is responsible for normal sensation of the areas in quesion. Certain postures can cause increased pressure one nerve and thereby result in numbness. It is import to report these symptoms and signs to your physician and request a physical examination to determine the exact cause and institute proper treatment.
See a neurologist. Your symptoms suggest pinching of the nerves in the lower back and neck. Neurologist may be able to find the source of preaching more precisely.