I am sorry that you find youself in this situation. You have not said whether your student loan was obtained privately or through a federally insured program. If the later, the debt is collected by the Federal Government. Unfortunately, congress has made the IRS a collector for various kinds of federal payments and levies through the Department of Treasury Finacial Management Program (FMS). The IRS does not have any discrection with regard to student loan debts reported through FMS.
What you will want to do is to obtain a hardship deferral, and have the deferal reported so as to remove or modify your account from FMS. An example, is an Economic Hardship Deferment Request submitted to the Federal Family Education Loan Program.
There may be some good news for you. The same FMS debt collection system works for you to collect back child support obligations. You should follow up with your local Family Court/DA office to make sure that unpaid child report is being reported to FMS. By doing so, you can put the IRS to work for you. Your ex-husband's tax refunds will be taken to pay his FMS debt and should eventually be paid to you.