@KoiwiGal - I think it varies from person to person, but one thing that always stuck with me is that those hormones can affect how attractive you find someone. When you're on the pill, I assume the luteal phase, along with fertility hormones and all the rest are affected. And there have been studies that women are attracted to one particular kind of man during that phase, when it's possible to become pregnant, and to another kind of man when they aren't in that phase. There are also studies showing that women on the pill are attracted to a different kind of guy than when they are off the pill.
Some doctors have even said that women should try going off the pill for a while before they marry someone, just to make sure that it's not the artificial hormones talking.
I think it would be interesting to just see if you fight more with your boyfriend when you are going through the luteal phase. Might shed some light on what your hormones are doing to your choices!