Sometimes babies changes positions I we can't feel them! I had an ultrasound last Thursday, and my baby was moving everywhere and I couldn't feel him at all! I was told that it was because of the position he was and at 21 weeks he's still very small, and has a lot of room on there
It is normal to have streaks if less frequent activity. As long as you can still feel baby move then things are going to be ok. But if you are worried, there is nothing wrong with getting an earlier appointment with your OB/MW and have them check you.
I would think that if you are feeling some movement its okay. But if you are not feeling any at all I would call your doctor or midwife and let them know. That's a perfectly valid concern and I wouldn't hesitate to ask about it.