I actually have MS (Multiple Sclerosis). Are you recently diagnosed? Recently LP?
Allow yourself to grieve but remember you are still you. I don't know much about fibromyalgia, I just know how I go about it day-by-day.
Can you take anything for the pain? Pain is a bugger and it is really draining. I have trained myself into a (quite) high pain threshold by using visualisation / breathing techniques to 'go elsewhere'. I have pretty much done this myself but I hear others use meditation. It is tiring though and not easy when you have a child.
I chose to ignore my disability as much as possible and refuse to accept limitations to my career, (I'm 'lucky' that my disability is mainly invisible and within reason I can still do this), I also find keeping my mind and body active pursuing my dreams helps me ignore the illness. Which in turn makes me less stressed and I believe that helps. I found massage really helped me, not just with stretching out my muscles but also my self-esteem (sadly I can't afford it at the moment).
There are plenty of unique things about you that are not fibromyalgia, find them and what makes you happy. But you have to be creative in your thinking, budget your energy and take short-cuts where you can.
Listen to your body, sounds like you have been overdoing things. And that's o.k. as long as it is a short-term thing over something that will make you happy long-term. (Unless your doctor disagrees - in which case believe him / her). Can your son help you wash your hair? Have you got friends you can ask to help?
Can you afford to get a mobile hairdresser to do it / visit a salon? I have found people have been remarkably kind when I have been in my darkest times. (Though my family are crap and have only just acknowledged I have MS and rarely help (I can count the times on 3 fingers and still have change) with anything - I have had it for 19 years FFS!) Be your own social worker, look at it as a problem, try to divorce it from you, and find solutions.
There is absolutely no shame in asking for help, even from your son, but recognise that if you take this route it will be hard on him and on your relationship. Be sensitive and listen to what he feels comfortable doing, and make sure he gets a chance to have a normal life / respite too and ask social services if he is eligible for carers allowance when he hits 16.
Someone I know with older kids has found a lot of support for her kids from a local group for young carers. Also check out holiday schemes and after school clubs. Ask CAB / School.
Social services (for you as an adult not for your child) and DLA are also key to all this - ask your GP for a referral as an adult. It will take a long time. Is there a disability support group locally? CAB would know.
One warning, I found even with help filling in the DLA form was a really emotional, humiliating, draining and degrading experience. It also has to be completed (with supporting docs supplied) in a tight time-scale (I think it is a month). Ask your doctor if he thinks you will be eligible first. If you can get someone from social services / a fibro / disability support group who has experience to help it wold be much better. Do you have mobility / fatigue issues? Would a blue badge help? Having one has helped me more than any single other thing.