What Could Painful Muscles With Low Energy Levels Suggest?

Hi, i have felt really tiered and achey bones and muscles for the past 2 years now, and its really getting me down. I have huge energy drops all the time, i have had loads of blood tests at the doctors but they cant find anything wrong. i am a 45 old female, and this is really restricting my life, i carnt work, or plan anything as i am so tiered all the time. i may have one or two days out of a week that i feel good.Regards chrissy