No baby movement

Im officially 21 weeks tomorrow. I've been feeling movement for about 3 weeks now, I'd say. Although I didn't know it was him until I saw him & felt him at the same time at my anatomy scan. He seems to sleep a lot, which is normal. But today I have felt no movement. I have been awake all day and relaxing. I'm getting concerned. I feel like I should've felt him at least once. Should I be concerned? Should I call my doctor? I'm kind of freaking out. I just want to make sure hes okay.