Catholics: two questions on papal infallibility and the immaculate conception....?

I go by scripture and there are no scriptures that speak about the infallibility of the pope (those I believe he is a respected leader of the Catholics) and none that teach that Mary was born without sin. She even says "I thank God my Savior", which shows that she realized she needed a savior. It is one of those doctrines that was put out by the church but can not be substantiated by scripture. Also, think about it, if Mary was born without sin, then her mother was probably also and down the line we go. It doesn't make Mary any less that she was a sinner. Only God himself (The Father, Son, and Holy Ghost) are sinless. If Mary was sinless, then she would be capable of saving us which we know is not true - only Jesus can save us.