how can I find my purchase history

Click on the link to 'See your purchase history in the App Store or iTunes Store' [iOS, computer, or web] - Does not include purchases made by others under Family Sharing; those have to be checked from their accounts. --> http://support.apple.com/HT204088

My itunes account balance keeps alternating between 19.27 and 1.21 on the screen. It starts at 19.27 then when I try to purchase a song it states I cannot purchase a song because the balance is 1.21. This has been going on for quite awhile and I cannot purchase anything. I have taken screen shots every time it has occurred.