I'd curved spine young but doc told me its not serious n no follow-up is necessary. However my right hip is half an inch higher than my left but I do not walk with a limp. Constant backache though. Is my back d cause?

Get a second opinion. Sometimes a second opinion can be very helpful particularly if you are having symptoms. Not everyone with scoliosis (curved spine) has symptoms, but if you do sometimes some simple measures can help.
Scoliosis. You need an examination by an experienced orthopaedic surgeon.
It depends. Mild scoliosis curves usually do not cause back pain, but the same patient with a mild curve can have conditions such as degenerative disc disease or a disc herniations. Similarly, leg length discrepancies less than an inch do not usually cause pain. A thorough physical exam can usually sort out the cause of your problem. Thank you for the question.