My hair is falling out terribly ? I had not very thick and abundant ha…

My hair is falling out terribly ? I had not very thick and abundant hair since childhood. But during pregnancy they didn't fall out at all and became thicker. Now it falls out in clumps? especially when I take a shower, I am terrified of my hair. It's like in horror movies happens. Exactly like that. I will soon be bald. What vitamins would you recommend? I am not taking anything right now.