Why was Christ's birthday changed?

I have always had issues with the Bible and thought about God but my life is in shambles and everyone keeps telling me to just believe. So I am coming to get help and understand. When looking into Christ, I have seen that his birthday was set for December 25th. But yet when reading the Bible it says that they follow the star of Bethlehem which this star is not present in the sky until June 26th. Please I want to believe but I need solid proof that this isn't just something people hold onto and this stuff is real and not fake.