What Causes Hair Loss After Childbirth?

Hi i am 28years old delivered my 2nd baby 4months back.during my 1st delivery i had no hairloss at all.this time after 3 months since i stopped feeding i noticed all of a sudden my hair just vanished from the front both sides has become very thin and half of what it used to be.will my hair ever grow back?i was told to take follihair and apply Qsera and anastim serum.plz help