Babies movements

Natalie
Hello! I'm 21 weeks and feeling my baby move more and more which is fab but there doesn't seem to be a consistent pattern yet. 
Does anyone know when you should be getting to know this pattern and therefore taking note of reduced movements? (I have read the Count the Kicks website for info and it's still a little vague on that front)
Generally I feel more when I am sitting down and a lot when I get into bed at night (like right now!) and sometimes after I eat. But I'm thinking it's because I am sat down and calm that I notice them more. It's hard during the day if you are busy or moving around lots! 
Any thoughts are welcome - big thanks :-) X