Yes, it could be your hormones, a skipped period isn't uncommon BUT Yes you could be pregnant if you're having unprotected sex!
You should probably take a pregnancy test. That's a much more reliable way to know if you are pregnant than asking us to guess :-P
If you are pregnant, congratulations! If you're not and don't want to be, it's probably time to look into a more effective form of contraception. If you don't like condoms and don't want to use hormones, read up on natural family planning so at least you can avoid your most fertile times.
In regards to pp who said you need to "stop breastfeeding ASAP" that is just not true. Continue breastfeeding! Your daughter MAY wean herself as your milk changes it's flavor as you get closer to the end of your pregnancy (it starts to be formulated for the NEW baby) but that can be up to HER.
HTH
T.