Urgent help needed

I am the first in my family to go to college. Without family support, I self-financed three college degrees (BA, MA and PhD) at state colleges between 1988 and 2005 using Pell Grants, multiple jobs, scholarships and $90,000 in subsidized and unsubsidized student loans.

My loans have been bought and sold so many times it is impossible to keep track of changes in rates, balances and terms of service since I have never had to resign any promissory notes. Eventually, I was able to consolidate the loans with Sallie Mae at a 7% interest rate. My loan payments have ranged from $400-600/mo. depending on the loan provider and lowest possible payment option available. 

...I am currently a public school teacher with an income of $50,000, barely enough income to pay the interest-only payments. I have never missed a payment in over ten years ... and my loan balance stands at $105,000. To date, I have paid over $40,000 in loan payments and because my income restricts me to interest-only payments, and the 7% daily capitalized interest rate, I now owe $15,000 more than I borrowed....

Please help in any way that you can