You have to look at weight loss as a lifestyle change. Something you will be willing to work at for the rest of your your life. Once you get to your ideal weight, you still have to eat healthy and exercise to maintain your accomplishments, so the keys are to start a journal, of healthy eating. Three healthy meals a day, and two healthy snacks. Walk as often as possible even if it's only for 5 min at a time. Then add 1 min increments until you reach at least 30 min a day. You have to find exercises that fit your needs. (no two people are exactly the same). Be willing to stick with it, but not over do it. Drink plenty of water. Consult with your Doctor to make sure you are health enough for exercising. Last but not least, make it fun. Find an accountability buddy to work out with rather it be a friend, an online pal, or family member. You are more likely to stick with.
Happy new lifestyle change to you. I know you can do it......

I try to ride my recumbent bike, I go to chair yoga. I can't do regular yoga or other exercises I can't stand long.

From what I read it happens to a lot of people though not sure of the percentage. It's a combination of lack of movement due to the pain and side effects from the medications. Also my rhuematologist told me there are two types of fibro. Just plain fibro and fibro that is a precursor to another autoimmune disease so weight gain could also indicate something else is going wrong. So she requires I do blood tests every few months to see if anything has changed.
I also think with our nervous system malfunctioning that might help in the weight gain. The other thing is that this thing is not one size fits all for this disease so the weight gain can be different for all too.
Right now I'm getting rid of carbs and sugars, not completely but eliminating as much as possible. And including more natural fats since I already had an issue with insulin resistance. And I'm getting rid of the meds. They not really helping and the side effects not worth it. Trying to handle it naturally by cutting gluten and as much chemicals as possible and trying to explain exercise.

Walking is the best way for us to exercise when we are able. I am wondering if a lot of women are over weight with fibro. I need to lose about 40 pounds. Just thinking it might be connected

I found that doing low impact exercise and working up very slowly like only a couple of laps of the pool for a few weeks and add once you feel ok doing it but not to push yourself also a little bit of walking if you can manage. Unfortunately I'm unable to do any exercise ATM as my everyday pain has increased