I have polymyalgia rheumatica which is an auto-immune condition, causing inflammation of large muscle groups. When it really hit me, I had difficulty getting out of bed, reaching the light switch (I had to head butt it) and just about everything else. The remedy is prednisolone, a steroid, in gradually reducing doses. I have had a few flares, on the way down and am currently back up to 10mg as my inflammatory markers were not responding as expected. Steroids aren't a cure but control the inflammation which enables the patient to get on with life. One day, the disease should 'burn itself out'. After almost four years, I still live in hope.
Sorry,*merlot*, I know I have digressed from your OP, but what I am getting round to suggesting is that perhaps you should ask your GP for a blood test in case there is an underlying inflammatory cause for your flares.