Targeted steroids - the steroids in nasal sprays like Flonase and Nasonex or in some asthma maintenance inhalers are different than taking a daily oral steroid like prednisone. A nose spray steroid will not make you gain weight. I've taken several several different nasal steroids, and never had a weight gain problem with them - and I've also never seen a reputable source that linked weight gain to a targeted steroid. There may be complaints with random people online saying that flonase caused them to gain weight, but I think those are likely cases of 'not my fault syndrome'.
I currently take three forms of targeted steroids - inhaled, nasal, and occular - since they act on the site, they don't have the same full body side effects that you get when you take a steroid like prednisone. (which I take frequently, and often causes weight gain and water retention for me.) In addition, a nasal steroid is better for you than an antihistamine, over the counter or not. The problem is your nose - the spray gives the medicine directly to your nose, not to your whole body. My allergist overwhelmingly prefers the nasal spray over oral medications - I need both, but he has many patients that just do the spray.
The steroids that are in a targeted med are nothing to be afraid of. But if you don't treat the inflammation with the targeted med, you may eventually end up with more intense inflammation that will have to be treated with an oral steroid, like prednisone. As someone who ends up on pred courses about 10 times a year - I can tell you that oral prednisone will cause you weight, as well as a host of other problems.
Starting over with my weight loss goals: 8/15/2011
Losing with challenges: Severe persistent asthma, multiple life-threatening food allergies, environmental allergies, gastric emptying delay, squishy esophagus, pancreatic exocrine insufficiency, left ankle arthroscopic surgery