What Causes Weakness In The Muscles Of The Limbs?

Hi I am 54 years old and for the last 5 years been to all kinds of Dr.'s. I was told I had ALs and then went to Mayo and said that I didn't. I have had all kinds of blood work and a MRI done on my spine. Mayo thought that it was a form of Muscle dystriphy (?) but the last blood test said it wasn't, I had a DNA test done, and they still can not figure out what it is and that was done in December 2010, Mayo is working with a Dr in Germany. I have very WEAK leg muscles and arm muscles, it is very hard for me to climb stairs and if I am on the floor I need something to push myself up. I have fallen also. I certainly have all the Dr's baffold, no one has given me anything for it, meanwhile I just get weaker and weaker, I read something about Lyme disease, I do have some symptoms but no rashes and no breathing problems. Any IDEA'S???? Colleen