R.J.
It usually lasts AROUND six months (read 3-12). Doesn't make a difference whether you're breastfeeding or not. The hormones stop our natural hair loss for 280 days (ish), and at a hundred hairs a day...that means we have to lose (yikes) 28,000 hairs. Thank the powers that be it doesn't happen all at once, or we'd all be fat and bald and crying in the corner.
Long hair & curly hair make it SEEM worse (long hair and you've got that spiderwebby thing all day, and curly hair means you're pulling out clumps in the shower -because it stays locked in the curl, even thought it's detached from the scalp- until showertime. Ugh). Short had has the most dramatic effect, because there goes the volume...and you've got the "itchies" all day. Sigh. So no matter our hair type we're screwed.
Number one cause of EXTREME hair loss after pregnancy is thyroid being wonky.
Number two cause is dieting. (Our bodies stop sending proteins to the hairshaft if we're starving ourselves...hence why anorexics frequently have dull, thinning hair)