It kind of depends on how long you nursed and how old your baby is. Regardless of the age of your baby, your hormones will be out of whack, your hair might start falling out, you may have stronger PMS and different periods than you did before. If you quit within 6 mos of having the baby or aren't sleeping well, I blame just recovery hormones. It took a good 14 months for me to return to the normally even keeled person I was before I had my non-sleeping first child. The duration of hormonal wackiness for me seems to be related to how long I nursed - i.e. my hormones are out of whack, still, after having stopped nursing 8 months ago with my second child who I nursed for 2 years. I'm not super emotional, but I do have real emotional swings, PMS symptoms and headaches that I never had before. I stopped nursing my first child at 14 months and it took about 3 months for my hormones to get back to normal. Those three months I had heavy PMS. again, I hadn't suffered from this before. So... you might talk to your OB. In the Bay Area, they'd send you to an eastern medical specialist for herbal teas to help get things back to normal.
Best of luck.