If your baby is 3 months old, and you are nursing on demand, you haven't missed feedings, you don't use a paci or bottle, the baby is still nursing at night- you are probably just experiencing weird hormones.
There was an article in LLLI on ecological breastfeeding that would explain it- or if you have TCOYF- there is a section in there about it as well.
That said- I didn't know that with DD. She was still breastfeeding, but slept through the night, and had started on solids when I got pg with DS (no period in sight). They are 15 mo apart.