maybe try to change the formula? 12 days is too long for babies not to poo. my baby is also 2m+ and the longest she didnt poo is only max 2days.
after every shower, try to massage his tummy gently with minyak telon/yu yee oil and do alot of bicycle motion(not only helps for gassy tummy in my opinion).
every play time, help him to sit and stand for a bit. it helps with peristalsis movement,same like adults.