I have a heart shaped uterus, can this cause irregular bleedings? I'm on the pill and this happens like 2 times a year

Shouldn't be. A bicornuate uterus (heart shaped) can have a septum or even a side of the uterus that doesn't connect to the cervix. If this were the case, you'd have painful cycles more often +/- abnormal bleeding. With your symptoms, I doubt the shape has anything to do with it. Continue the ocps and occasional break-through bleeding is to be expected. Twice a year is not bad.