I have 23 years experience as a Lactation Consultatant and a Family Planning instructor, so I can tell you the possibilities and a couple pointers here:
1) Any breastfeeding woman CAN become pregnant. The possibility is lessened in women who *exclusively* breastfeed, no bottles, no pacifiers, and breastfeed completely on demand. This also includes keeping baby close to Mom 24/7. Very few American women mother in this fashion, so their hormone levels are not sustained at the level needed to suspress ovulation.
2) In about 80% of women, there will be a "warning" period before ovulation occurs. This may be what you experienced with the light bleeding, though not necessarily. In any case, ovulation can be detected by women trained to notice it--you have probably noticed it in the past anyway. All women have a cervical discharge of mucus that is similar to egg whites that occurs after a thicker mucus; that's the hallmark of true ovulation. Usually with breastfeeding this thicker mucus lasts quite awhile, as if to warn you that your body is gearing up to return to "regular use."
3) If you have in fact ovulated, if this description in number 2 makes you say "uh-oh" and that was around 2 weeks ago, make yourself feel better by doing a home pregnancy test.
I hope this has helped a bit, I could go on and on, but don't want to bore or overwhelm you! I'll be thinking of you, K.