I think I might be adopted,because my parents are always treating me different than my sisters,also we don't look alike,and there is no pictures of my mother being pregnant with me. I don't know what to do,and they won't answer my questions. I already found ouer blood types,and they could be my biological parents. What do I do now?

DNA testing would be the only sure fire method available, or simply ASK THEM.

I don't look like my siblings. Out of thousands of pictures, not one shows my mother pregnant with any of us. She probably wouldn't let her picture be taken.
How old are you? Many kids go through a stage of wondering this. Do they just clam up when you ask, or do they tell you that you are silly? Have you been to the Town Hall to ask for your birth record or applied to your state for your birth certificate?