How long does hair normally take to grow back in a healthy person with no hereditary hair loss?

Hair grows at a rate of about 1cm or more a month.  After your hair is pulled out traumatically, it may take a few weeks for the hair follicle to start to generate a new hair.  If the same hair follicle is traumatized repeatedly, it may never generate new hair.  This is called traction allopecia. 

If you pulled your hair out traumatically, then expect the follicle to be dormant for a few weeks.  After that a new baby hair will sprout and slowly mature over the course of several months.  The rate of growth is about 1/2 inch every month.  Assuming you have no other conditions, your hair should grow back.  If it doesn't you should be checked out by a doctor.

After yanking out a hair, a new hair gets produced within 2-3 weeks. In response to your second question, it's not possible to state the cause of increased shedding without seeing your scalp up close and knowing your history from A to Z and seeing all your blood tests.