One way to "know for sure" is to look at a chart. If you have not started yet, then begin jotting down daily notes of your cervical fluid. Do you know how to check your cervix? This can be helpful, too. Sorry to hear your class was postponed. You can proably call your local NFP instructor for a quick "review" of what to look for. In the mean time, there are some great NFP primers online. Please browse through this topic for past posts which cover the basics. There are direct links within the posts.
From your PMS-type descriptions, it sounds like your menstrual cycle may be returning. Most women experience a warning period as their bodies become fertile again; however, there is a small likelihood that you could become pregant without a warning period. Just so you know. Some folks are super fertile! Without knowing exactly how often you nurse Toni during the day, or seeing your charts, I cannot make a bonafide call on this...but, if Toni is sleeping at night as you say, then you're probably not breastfeeding frequently enough to experience LAM - lactational amennoreah(sp?). I'd say your fertility is returning.
Check out the posts on LAM and ask your NFP instructor about ecological breastfeeding. You can postpone pregnancy by breastfeding, but frequent, on demand suckling is key (nighttime nursing and pacifier use are other factors).
Kippley's book is THE best resource. Here is a quick link to the book on Amazon, and it's chock full of reviews...http://www.amazon.com/exec/obidos/tg...glance&s=books