weight gain on arimidex anyone?

Need some input from anyone on Arimidex.  Who is experiencing weight gain?  Since I've been on it, I've gained probably 20 lbs.  I'm only 5' 1" so it's a lot on my frame.  I work out at least 5 times a week at the gym doing almost an hour on elliptical and about 20 minutes on weight training.  Additionally, I do the treadmill at home beofore work a few days a week for 30 minutes. I totally watch what I eat, not over indulging on fattening foods.  Keep to very low sugar and carbs and high protein with a cocktail or two over the weekend.  Still can't take off the excess pounds.  Very frustrating.  Not really complaining because I am very blessed to be able to have this drug to keep my cancer away, just wondering if anyone else finds this to be a side effect.  Love & hugs & good health to you all!!