My ipod classic 80gb only allows music from 5 itunes accounts!!?

So i have the newest Ipod classic. And lately whenever I want to add music to it, my itunes sayss that i can only upload music on my ipod from 5 itunes accounts! I've added music from my other computer, my sisters account, my boyfriend's account and my cousin's account. That's only 4 accounts, but when I try to add music from my account it won't let me! I understand what apple is doing, so we buy more songs. But I just bought 4 songs on my account, and it won't let me add them! Is there any way i get my music on my ipod? Help, this is really frustrating, and i want more music on my ipd
The computer i'm on now is my sisters account, so the accounts are
sisters
boyfriends
cousins
my other computer, which no one is signed into on itunes

thats only 4