Waalaikum assalam! At 21 weeks, baby movements boleh rasa anywhere in that area lah, some moms feel it lower near the bladder, some higher towards the belly button, depends on baby's position and where your placenta is sitting. I'd say just enjoy feeling those little flutters, but if you're worried about where movements should be or if you notice something's off, best to check with your doctor next visit just to be safe.