I am not even kidding when I say that from 18 weeks to 20 weeks, I look like a different person. (Or my midsection looks like a different person's midsection, anyway.) I was definitely looking chubby before, but lately I've really blown up.
Also, are you wearing maternity clothes? I have mainly just been wearing my regular clothes that still fit, but I went shopping for maternity clothes a few days ago, and that made a HUGE difference. My regular clothes were just cutting into the middle of my bump and making me look chubby. Maternity clothes accentuate my bump and make me look pregnant.
But give it a couple more weeks and I bet you'll be showing a lot more... things change quickly at this point!