Dear Sir, At the age of 18, a weight of 100, needs evaluation of your hormonal status, consulting any dietician or therapist will be of no help unless a cause to your obesity is found. so the first step you need is to consult an endocrinologist and get evaluated for the cause of obesity, only then will you be able to take steps to reduce and manage it.

Ur weight itself is the solution for ur problems.  Reduce it and so reduce ur pain.  Take analgesic like tab enzoflam twice a day for five days.  See an obesity specialist doctor for reducing weight and physiotherapy doctor for exercise.