Hi Liisa. We have subforums specifically for each of these drugs. You might want to check them out and browse. Each of these drugs have their own side effects and affect people differently, so that will help you get an idea of how people have been responding.
As to the weight gain - generally it's not the drug that makes you gain weight, it's that taking the drug makes you hungry, leading to you eating more, which makes you gain weight. As long as you watch what you're eating and make sure you don't eat more than usual, it should be fine. Some people weigh more while they're on it because of water retention, but that's not weight gain per se, just water weight.