I lived in a house w/ a water leak under it for 6 yrs. I have been diagnosed w/ chronic myositis. Could this b the cause?

Possible. Chronic humidity and or allergies may cause muscle aches. But there are many other causes as well.If you can afford stay away from that environment for few weeks and see if you feel better, if not must see a doctor.
No. Myositis, if you are using the term correctly is a disease characteriazed by muscle inflammation. It is not related to a water leak.