You might luck out. I got 2 periods when ds was 2 and 3 mos old, then nothing until he was 10 mos old. I do think I got those 2 early ones b/c we were having problems, so not the same situation. Congrats on the new little one, though.
I get mine back quick like that too! I exclusively bf and cosleep (did the first 3-4 months...don't now) too. With my 2nd dd (can't remember how soon I got af back w/ 1st) it came back at 7wks pp. With my 3rd, it was 6wks pp. And it's been regular ever since.
The same thing happened to me...I got (what I assuemd) were light periods at 7 and 9 weeks post-partum. However, since then, no sign of AF, and Aaron's now 4 months. I actually got so paranoid I did a p/g test last week, since I thought once it started back it would be regular. Evidently, the b/f does all kinds of weird things and regularity isn't to be expected.
On the other hand, you do have to assume you're fertile now!
I quit bleeding at 2w6d pp, and haven't bled since but I'm worried af is going to show up earlier this time (with dd I got six months off). I had a horrible migraine last night complete with vomiting and rarely have them while pregnant or nursing. I'm hoping was something environmental (I have food and perfume sensitivites) and not hormonal.