I know exactly how you are feeling... but for me it was later in my pregnancy. I would go for hours and sometimes days without feeling the baby. It happened really from 22-30 weeeks.( &some towards the end) I would get myself all worked up and then I would feel her move and it would ease my mind again. I never told anyone about it because I thought they would think I was over reacting! But it was really strange. I will tell you this my pregnancy with my 1st DD was the same. That's why I thought this baby might be a girl too! My boys were so active so early and never stopped! So maybe you are having a girl!
I know it will put your mind at ease when you hear the heartbeat. I would tell you not to worry but I know how hard it is! Sometimes they say it's how you carry the baby.(where the baby is position or maybe it's a small baby) I know I read everything I could find on the internet. Well, this past January I gave birth to a very healthy baby girl. Who doesn't stop moving now!
Enjoy your pregnancy!!!