Im losing so much hair! when i brush it, shower, play with it, a handful of hair comes out. what would this be from and how can i stop it?!

Hair loss: Medical causes for hair loss could include: hormonal problems (low thyroid), seborrhea, alopecia areata, stressful illnesses. For most people, hair loss can be worked up by one's primary care doctor - they'll probably check your thyroid and for anemia. If no medical problems are found, then one can see a dermatologist. Best of luck!