Weight loss during pregnancy

So far I'm 13 weeks 2 days and according to my doctor I've lost 20 pounds since my first appointment. I think one of the measurements was off though and it's 15 pounds, but either way he says it's too much and I can't lose anymore. I have not been nauseated or thrown up the entire pregnancy, however I do get full very fast but I think I'm eating more than before I was pregnant. Has anyone else experienced this?