20 weeks pregnant, should I be worried baby is moving a bit less?

I am 20 weeks 4 days; I had my ultrasound last week, and my baby boy is healthy. I was told I had an anterior placenta. Well a few days into my 18 weeks, my baby started kicking (as he is breached, or was when we did US) and I felt the kicks in my low pelvic area. They were pretty strong that my bf felt it too from the outside! He kept kicking around the same spot few days after that, especially when I went to bed or when I would wake up in the middle of the night/morning. Now 2 days ago, I stopped feeling his kicks. I kinda feel a little rumble here and there, but not as much or in the same spot. Should I be worried? Did he maybe switch position and because of placenta, I can't feel much yet? I have my next appnt this coming Wednesday.