i've been on one form of birth control or another for 14 years now ... the last 6 years have been on exactly the same pill (generic for ortho novum). and the simple answer is yes, it is possible to ovulate while on the pill, even if taken correctly.
basically that 1% or whatever it is chance that you can get pregnant means that there is a chance you can ovulate. i feel as though i ovulate maybe once a year or so. i have a bit of spotting and it feels like my ovaries are mad at me.
what i suggest is pop a couple tylenol (don't do advil/ibeprophen if you're spotting though ... it has a blood thinner in it, so it has the potential to make the spotting worse) and use protection if you're having sex. it is still unlikely that you would conceive, but you're obviously a little worried about the situation, so extra protection is never a bad idea.
good luck and feel better!