Start by just walking a short distance daily. Increase distance weekly as you feel better. No need to do a bunch of ridiculous appetite boosting workouts at this stage.
Try removing gluten, sugar, and anything artificial. Research Clean eating which will tell you more. Basically the less processed food the better. Best wishes!
If you've checked with your doctor, you should probably be doing some exercise every day, as that, typically, helps keep your muscles from getting so sore and stiff or if they're already sore and stiff, exercise can help limber them up a little bit.
Fibromyalgia symptoms are often linked to hypothyroidism and obesity/weight gain/inability to lose is a prime symptom of hypothyroidism, as is muscle aches/pain, weakness and fatigue/exhaustion... If your thyroid hormone levels haven't been tested, you should talk to your doctor about getting them tested to make sure that's not your problem, as adequate thyroid hormones can go a long way toward helping you reach a weight goal.