21 weeks and still don't "feel" pregnant

I had a rough first trimester, but the second trimester I've had no symptoms really at all. Except heartburn, which I had before the pregnancy. My tummy isnt extremely big or round, and I don't feel any kicks. I try not to freak myself out, but I can't help it sometimes. My last appt I had at 18 weeks and we saw a healthy baby girl! But my next appt isn't for another week and a half and I'm pretty nervous. Am I crazy?? Please help