why do i have to wait 90 days to get my items that i have paid for from iTunes

why do i have to wait 90 days to get my items that i have paid for from iTunes.i been trying add music from downloads and get this message everytime i try to download my purchases or this com can be used with different id in one day. if i change my apple id how is it going to recognise my past purchases this dors not make any sense to me