I’ve been told to start counting kicks

I’m 24 +4 today and just had an appointment with my midwife, I told her that I noticed little girl wasn’t moving around as much and she said that I should start counting kicks now. I thought you weren’t meant to until 30ish weeks?

I’m also waiting to talk to a specialist because my BMI is low and they want to make sure she’s growing okay. My blood pressure was also low today at my appointment. Can anyone give me some advise?