I am taking cymbalta (duloxetine) for fibromyalgia and have gained 20lbs with hand and feet swelling. Are there other drugs that treat fibromyalgia with less side?

Make sure is Fibro. Fibromyalgia is one of the most overly diagnosed condition today. There are many underlying conditions that can explain many of the symptoms that are more common-place and actually treatable. Conditions of the neck and low back will frequently have "myofascial" (muscle, tendon, ligament=soft-tissues) related pain that will spread quite far at times. Seek pain specialist eval. If needed for options.
Hands/feet swelling. Weight gain is not a common side effect from duloxetine [cymbalta] treatment of fibromyalgia syndrome [fms]. The combination of weight gain with swelling of hands and feet suggests another condition [eg, kidney disease, heart disease etc] or another drug [steroidal, non-steroidal antiinflammatory, pregabalin, etc] used at the same time or even in the past. You should see your physician soon!
Possibly. All medication have side effects. There are a number of medication that are indicated for fibromyalgia. Lyrica, savella, (milnacipran) effexor, Pristiq and muscle relaxants have all been shown to be helpful for fibro. Regular, moderate, non-impact aerobic exercise and cognitive behavioral therapy have been shown to be as if not more effective than medication and have almost no adverse effects.