I am taking mainly naproxen 500 mg twice a day and 20 mg Amytriptylene for fibromyalgia pain. It does help, but I have put about 16kgs since sept 14. I need to lose weight but it's not coming off. I am finding that my legs feel different, as if they're no

Diet and exercise. The amitriptyline dose is low and likely not related to weight gain. Aerobic exercise is a very important part of the treatment of fibromyalgia so you need to start a regular exercise program. You also need to minimize carbohydrate intake and control portion size to lose weight.
Aquatherapy. 53y fem. W. Fibromyalgia/obesity uses NSAID/tricyclic. Obesity etiologic co-factor for FM & must reduce. Weak/spastic muscles render land based exercise too painful. Buoyancy of water enables soft tissue exercise for greater muscle mass/tone. Lyrica, Savella (milnacipran) or Cymbalta useful for pain control; enabling greater exercise. Possibly useful: Hops extract, Cannabis, Yerba matte & Ribose. Avoid carbs.