Aiyoh, jangan risau sangat lah, memang banyak babies do this phase! A few of my mum friends' babies also did the same, ketuk-ketuk kepala sendiri bila meragam or bored, and sekarang semua fine je. It's actually quite common around that age, mungkin dia tengah explore sensations or just being fussy, but since you're already worried, mungkin baik check dengan pediatrician just to be safe and get peace of mind, terutama kalau dia ketuk dengan kuat atau ada symptoms lain yang unusual. Your adik ipar is right that it can be normal development, tapi better to have a doctor confirm so you can relax properly!