How can I stop hair loss IMMEDIATELY?

I am 17 years old and shedding like a dog. I eat and sleep regularly, have not had chemotherapy or anything like that, and have even started dying my hair with henna and avoid brushing it too much between washes. NOTHING is helping. I hope you understand what a catastrophe this is to me and won't try to advertise stuff that doesn't work because I seriously don't have money to throw away and if I don't figure something out right now I'm going to be practically bald by the time I'm 21. :( help me please!!!