this happened to me also and continued for a year. I would suggest sticking it out for 6 months then deciding if you want to take it to the on year mark based on continually overviewing your progress and seeing if you're imroving or deteriorating. Good Luck
the regrowth never caught up to the shedding so at the year mark i feel im more in the hole than before, so i discontinued using Propecia for this and other reasons