I'm also a federal employee, with USDA. I don't know which dept you work for - but are you eligible for Voluntary Leave Transfer/Donor Program? Its where if you have a medical emergency, you can put a request in, if you're approved other employees can donate leave to you, for as long as you need it. I have co-workers who have cancer and been on donor program for over a yr. See the link below for info. The lower link is for fact sheets on different leave options. HOpe this helps.
You can check with your HR staff or supervisor for info on this, if its available for your dept.