Same thing happened to me, i even lost weight during the same time, but once i hit 21 weeks, my belly just blew up lol i am 23 weeks and i am definitely starting to show. My baby girl moves so much now and i finally gained 3 pounds from the weight i started. They do say that in the 2nd trimester you start to feel like your self again, so just be patient and enjoy feeling better. But always email or call your doctor if you have any other concerns.
My symptoms stopped at week 13th and by week 17 I didn't feel pregnant at all. I am 31 weeks pregnant and my boy is healthy and active. The second trimester is supposed to be the easiest trimester to get through but If you are really concerned talk to your Dr.