We all gain differently. Those in the 20-something weeks, 14 pounds is what you should be gaining, it's not a lot at all if you had a normal BMI to start with. With DS, I gained most of my weight in the 2nd trimester and almost nothing the last month or so. Anyways, for those of you who want to obsess over numbers, check this site out.
You can enter your prepregnancy weight and your height and calculate to see the minimum and maximum weight gain (knowing it may be more or less because we're all different). Kind of a fun tool.