I BF'd my first and tried to take the mini-pill half way through (baby was 6 months old). I turned DEMONIC with the mini-pill. I was taken off as soon as I told my doctor. She said it isn't right for everyone.
It is only one of the two hormones that are in the regular pill. It is a hormone and will affect your moods (just like PMS).
It could also be PPD, but my guess is that it is the pill. Now that you are no longer BF'ing, your hormones are shifting again and it sounds like you are off kilter. Talk to your Dr. ASAP, I bet she puts you on a regular pill and life will be good again. :)
I am still BF'ing my second and when she started to self wean and eat solids, my cycle changed completely.
It is amazing how much our bodies change for these little critters. :) Best of luck to you!