What does this mean?

Maggie
For the past 2-3 months a few weeks before my period I've had real bleeding and cramps about a week and half before my period.. I have ulcerative colitis and I've read online  that can affect birth control. My OB said to come in to change my birth control.. Why would this be happening? It's so weird! Does this mean that my birth control maybe isn't strong enough? Idk! No I'm not pregnant.. No chance.