Cannot sign in to iTunes

When I tried to sign in into iTunes, it kept on saying that "incorrect password" and then I changed my password several times, and it still tells me that it is incorrect. It kept on repeating every time i tried. I do not know it is my macbook or my account, but I can sign in in my iphone and apple websites and icloud. I believe it is my macbook, so I was wondering if anyone had this problem and knows how to fix it.