Baby movements!

Carly
Hi! I am going to be 21 weeks tomorrow with my first and for the last week have basically felt the baby moving around/kicking one to two times a day. Friday I didn't feel her much and yesterday I didn't feel her at all.  So now I'm freaking out. I have a Doppler and heard her heartbeat yesterday.  Am I suppose to be feeling her daily at this point?? Or is it normal to go a few days without feeling her!! Any input would be greatly appreciated!!!