Why do i keep dropping hair , no matter what product i take orally or apply on my scalp?

i have tried garnier anti hair loss shampoo , and it got worse, tried hair plus shampoo and it got worse , tried hair plus tonic and garnier tonic and got worse , tried the hair push tablets and my nails are not so soft already , but hair still keeps dropping , tried he shou wu (radix polygoni multi flori) and it reduced the dropping at first then the effectiveness wore off after some time like three months , so i can't use he shou wu anymore , i tried taking ginseng (gao li sheng ) , it did reduce at first , then the effectiveness wore off again . i'm only 21 and the the top of my head at the back is gone , how to stop the hair loss now???