Do you know how birth control pills work?
Yes, I know how pills work. They don't mask every single symptom related to your cycle though.
They do, though. You'e not cycling on BC. Yes, you may have symptoms related to the hormones in your BC, but they aren't symptoms related to your non-existent cycle.
ETA: When I was on BC, I was even keel throughout, even when I was on my placebo/withdrawl bleeding week. I came off and my emotions were everywhere, I had acne, bloat, sore boobs, everything. It seemed like it got better after a few months, but I think that maybe I just got used to it and adjusted accordingly. For example, knowing the reason I was yelling at DH about something irrelevant and nitpicky, was most likely because I was PMSing.