I am certainly an early show-er.
I'm a size 8-10.
With my first pregnancy I had a little bump at 8 weeks.. Then with second I had a weeny one at 6 weeks. Third by 5 weeks, 4th right on 4 weeks and 5th / current 4.5 weeks. Yet I have friends who didn't show until 20 weeks. We're all different.
As for the weight gain, that does seem a lot in a small time frame so early on.. Have u just been so hungry? Eating wrong stuff? Or it's coming on regardless?
I can't really help there as only one of my pregnancies went beyond 23 weeks..