Aww, don't worry lah, every baby has their own timeline! Since you're already doing plenty of tummy time, that's the best thing, just keep at it and let baby build that neck and shoulder strength naturally. One of my mum friends' baby didn't roll until nearly 7 months and now she's everywhere, so really takde perlu stress. That said, if you're feeling worried or notice other things like baby seems stiff or tidak meeting other milestones, boleh check with your pediatrician just to be sure everything's progressing okay, they might suggest a bit more physio play or give you peace of mind, which is always good as a mum!