My hair has been falling out for about 6 months now when I run my fingers through it a considerable amount comes out. What can cause this!?

Many things. Hair "turns over" faster than just about anything else in the body, and many things - from illness to injury to surgical procedures to hormonal imbalances to infections to stress - can interfere with the normal hair cycle. Don't waste your money on tonics and "hair vitamins". Let a dermatologist go through the possibilities and find the cause.
Hair loss. Telogen effluvium is a form of nonscarring alopecia characterized by diffuse hair shedding, often with an acute onset. A chronic form with a more insidious onset and a longer duration also exists.[1, 2] telogen effluvium is a reactive process caused by a metabolic or hormonal stress or by medications. Generally, recovery is spontaneous and occurs within 6 months. We treat with B12 shots.
Be seen. Thyroid problems and stress are the most likely causes. See your doctor and they can do simple blood tests to check your thyroid and a host of other causes that are more rare.