I was given lexapro but I am too scared to take it. However, my mom was put on it and it helped her significantly and she didn't gain any weight at all (she did gain with others like Paxil). For the first week she felt a little sick, with headaches and slight nausea but all of that went away after a week or so. She also said it worked pretty fast, after only 2 to 2 1/2 weeks, although it can take up to 6 weeks to take full effect. I wouldn't worry too much about the weight gain, you should be fine. Goodluck with that!
~Isabella~