Here’s how each ordinary and extra payment is supposed to work: Money first goes to fees (late penalties, processing, consolidation, etc.), then to accrued interest, then to principal balance.
So let’s say you have a $10,000 loan at 5% annual interest and $20 monthly consolidation fees. After 10 days you make a $100 payment. The balance has accrued interest of $10,000*(.05/365)*10=$13.70. So when you pay $100, $20 goes to fees, $13.70 goes to interest, and $66.30 goes to principal making your new balance $9,933.70.
You make another $100 payment 10 days later. Balance is now $9,933.70+$9,933.70*(.05/365)*10=$9,947.31. $0 goes to fees (already paid this month), $13.61 goes to interest (notice it’s smaller than your last payment), and $86.39 goes to principal for a new balance of $9,860.92.
Your problem last year was your payments were so small, you weren’t breaking through the fees and interest to knock down the principal. IBR can be useful for those who are truly struggling and desperate, but you should definitely try to do more if you can.