I have tightness and pain on the back of my legs in the thighs. Pain on left side back of thigh and tightness in back of other areas of both thighs.

Common complaint. What is your usual level of activity? Have you done any extra-ordinary exercise? Walking up stairs? Heavy lifting? All of these things can cause 'tightness.' Usually just muscular in nature. Of course if you're having other complaints like foot weakness, instability of your gait, difficulty/losing control of urine - bowel ; you should see a doctor.
Pinched nerves. consider lumbar spine problem pinching nerves that go to the legs.