Edema and Fentanyl Citrate

I've gained 11 lbs in a month (not from eating like a pig) since I started taking Fentanyl Citrate. When the oenology nurse poked my finger the other day, blood just dripped out. My question is: Is the Fentanyl causing that much fluid in my tissues? And what can I do to get rid of the problem since its helping me more than anything I have taken over the last five years. I feel like I have my life back now since I'm out of bone pain.