I'm no expert - I am 26 weeks into my first pregnancy but I've noticed this too! I think they just have some days when they are more active than others and I think if they are facing towards your back then I think you can't feel the movement so much.
It's a bit disconcerting when you are used to feeling lots of movement! ]
I am 23 weeks and have been experiencing the same - apparently my placenta is anterior (at the front) so I suspect it blocks a lot of the movement. I think it is normal at this stage to have active and quiet days.
I noticed that the more active I am, the less is the baby. I'm wondering if it's to do with walking around and movement- the baby is rocked within the womb and sleeps more. (Also maybe when I'm more busy I pay attention less to potential movements.)
When I sit down after meals, he goes crazy. And of course at night.
As long as you feel 10 movements a day, it's fine!
I get the same. Im cursing her when she wont stop wriggling and kicking me in the bladder but when she goes quiet im shouting "move, please move to let me know you're ok!"
Is there anything she responds more to? Mine loves DP playing the guitar and twinkle twinkle off her cot mobile. If im panicking about her not moving, i lay down for 10 mins and breathe deeply - if she still wont move i get DP to play the guitar or if he isnt there, i get her mobile - does the trick!