For a few months my toe nails have been breaking off all most completey off with no pain at times I don't even notice it breaks off. What is causing it?

Few things . Can cause this. Fungus or trauma (even micro trauma) are some common reasons as are vitamin deficiencies. (microtrauma can occur by ill fitting shoes.) see a podiatrist who can help make the diagnosis and offer a treatment plan.
Malnutrition. I would suggest that you talk with your doctor asap -- you may have some kind of malnutrition perhaps involuntary due to some malabsorption problem. The symptoms you describe is usually caused by mineral and electrolyte imbalance --.