It is normal to put weight on after quitting anything I think, even alcohol which actually has calories in it! My diet is apalling at the moment. I have very little real appetite, but just crave sweet stuff. And I've never had a sweet tooth!
Also, is 20lbs that much if you were underweight before - it might be what you needed to gain. Sometimes we have such a distorted image of what is a healthy weight because of what we see in magazines.
Find out what your BMI is, and if it is in the normal range, give yourself a break, and carry on eating healthily and exercising. You've come a long way!