I struggled for years with similar problems. Instinctually you know the truth, but when the truth is ugly it's really hard to accept. It certainly doesn't help if other family members deny that it ever happened. I have four brothers and a sister and none of them were abused in the manner I was, nor do they acknowledge that I was abused. I now am confident in my memories, though I still often wish that I did not have to accept them as part of my reality.