I've been using a serum for the past 4 months, but now I've noticed that my hair has become really weak. It falls out if I even run my hand through it, and it just feels so fragile. I realize I was applying it wrongon my scalp and before combing my hair. I've stopped using it now, but what else can I do to help strengthen my hair quickly?

Yes you can use it no problem, visit Dermatologist for appropriate treatment