im having major hairloss?

Im in desperate need for help for the past 2 months maybe 10 strands of hair are falling out when im doing nothing and a clump of hair is falling out in shower and when i brush it i had very thick hair and the texture has completely changed havent ever colored it in my life i have been using this keratine shampoo and i was washing my hair today and first i used my dove shampoo and no hairloss when i put the keratine bunch of hair fell off im close to tears right now im hopeless and idk how i make my hair grow back to what it used to be please help whats the cause of this and how do i make it stop