When does shedding from Big 3 start?

[win200]

I started using Propecia 5 weeks ago, Nizoral 3 weeks ago, and Rogaine 2 weeks ago. Obviously it's highly probable that I'll shed, but I'm wondering how long after beginning treatment that usually starts. I'm shedding now, but I don't know if it's attributable to the shedding that was happening already, or increased shedding from the meds.

And how bad a hit should I expect my hair to take, temporarily, while I go through the initial shed?

Thanks!