Flonase Side Effects: weight gain & feeling crabby. Migraine headaches http://www.medications.com/effect/view/14977 weight gain & feeling crabby. Migraine headaches I had the same problem and I felt horrible. I took it for about Sun, 16 Nov 2008 16:26:48 -0500 http://www.medications.com/effect/view/14977?item=14555 I had the same problem and I felt horrible. I took it for about 3 weeks before I realized what it was from. How long does it take leave your system? Do you still take it? http://www.medications.com/effect/view/14977?item=14555