Fetal movement patterns at 21 (almost 22 weeks) - is this normal?

Hey everyone! I'm pretty sure this is normal but I just like hearing stories from other women in the same situation as me. Like my question says, I am almost 22 weeks pregnant with my first baby. I've been feeling little movements since I was 16 weeks (my placenta is posterior so I can feel movements easier). Ever since I was 20-ish weeks I have felt kicks and wriggles every day, but some days I go hours without feeling much of anything. The baby is most active early in the morning, like until lunchtime, and then late at night. Is this normal to go hours without feeling anything? Sometimes I get really worried. I had an ultrasound this past week and everything was 100% normal...heartbeat was great & baby was measuring right on target. Any advice would be appreciated! :)