Need advice ladies!

So I need to lose A Lot of weight. Not just for my health but also for my babies health when I try for one in the future. I have fibromyalgia which means, for me anyway, everytime I exercise and lose weight I have a flare up and put it back on. So I was wondering if anyone has any tips to help me with this so I don't keep having flare ups and putting it on. I need to take control of my life but need advice on how to battle the fatigue and constantly getting ill!