Why do my joints hurt. could it be autoimmune disease?

Could be: Your joint pains could be caused by many things, and autoimmune disorders are a possiblitiy but not necessarily the cause. Simple arthritis, to rheumatoid, to lymes disease are other possiblities. The long and short of it is, you need to see a dr. For a clinical evaluation and get the proper testing and diagnosis to be sure, and then get the proper treatment. Good luck.

Impossible to know: This is impossible to answer without an examination and appropriate lab work. See a rheumatologist.