Hi, HMg, and welcome! I'm so glad you found us and joined in! We have a wonderful group of people who love to help one another and, as a bonus, really do care about each other too. I think you will like it here.
I really love all the "encouragement" your doctor gave you. 
It doesn't have to be a vicious cycle and you definitely are NOT fighting a losing battle! I've been there and done that! Having three children, quitting smoking, and living in the northern climates, I piled on the weight, too! It's easy to do...especially if you live in the north. You are so sedentary in the winter because it's just too darn cold outside. Having fibro and also carrying around a lot of extra weight means even more pain. I just reached a point that I didn't want to live in that body anymore and I was going to do something about it.
I started counting my carbohydrates. I didn't eliminate them but I kept a close count as to how many I was eating at a meal and limited them. I stuck more with lean meats and veggies. I also used a smaller plate. The dinner plates these days are huge! I have some dishes that belonged to my GGGGGrandmother who lived in the early 1800's. The dinner plate is about the size of today's sandwich plates! Remember, these people were farmers and clerks and worked very hard all day and were thankful to have food to put on that small plate! That opened my eyes. I also "divided" my plate so that the carbs only took up 1/4 of the plate. Half the plate was veggies. This all helped and when I would step on the scale and see that I at least didn't gain weight and most usually lost a little, that gave me incentive to continue.
I needed to add exercise to the mix. I had plantars faciitis, also, in both feet. Once I started wearing Birkenstock shoes, it cleared up...took several months though. Then I could walk and I walk daily now as a form of gentle exercise. Swimming or water exercise would be great for you right now until you get the plantar faciitis cleared up. It's gentle and good for fibro, too. These gentle exercises help kick in the metabolism so it will start to burn calories. Yoga is another good exercise. As Shirley said, be sure to start out slowly and work in to it.
If you live in the north and have all that cold and snow, you can get walking-in-place videos that are good...boring but good! 
I have one by Leslie Sansone. If I do it for 15 minutes, it's equivalent to walking one mile! There is a little aerobics at the end, too, and this really helped me lose weight, too. She has many videos to choose from, also. Just google her name and you will see all she has to offer.
I was in my middle 50's when I started this and was able to lose 85 pounds and keep it off. So, if you are an older person, don't let anyone tell you that you can't lose weight because you are older. It can be done and it was painless, too! I didn't deprive myself of any type of food. I just ate smaller portions.
When you get some weight off, you will have more energy, zest for life, and you should have a little less pain. I know that carrying in a ten pound bag of potatoes can make my arms hurt so just imagine what I was doing "carrying" 85 pounds around...ALL of the time! Yikes!
So, you really CAN do this and nothing is impossible. The only way it's impossible is if you don't try at all. Nothing gets done that way.
If someone asks you if you are alright, just say I'm fine. If they want to know what is wrong, just say you suffer from a chronic pain condition. You don't owe anyone an explanation either. Do you go around asking people what is wrong with them? I know I don't! If I see someone struggling, I don't ask what their problem is. Instead, I ask if I can help them in any way. So, don't let these "bores" bother you.
You are a great person that happens to have chronic pain. You can have a full and enjoyable life in spite of fibro. You do have to learn to pace yourself but you can do just about what you used to but in a different time frame. Fibro can make your life more challenging but it definitely is not a "losing battle"! I have traveled to Europe several times, walked on glaciers in Canada, snorkled in the ocean, and even parasailed with fibro. Live your life! You have a great life ahead of you and don't let fibro or any person's negative thinking and statements steal that away from you!
I'm looking forward to getting to know you better. Don't hesitate to ask questions because we are here to help you. I hope to hear more from you soon.
Sherrine