Taklah, 5 bulan baru okay je dia belum fully duduk sendiri, lagi-lagi kalau dia premature 36 minggu so adjusted age dia lebih muda lg, tulang belakang dia mmg still soft dan tak kuat enough nak support kepala properly, tu lah kenapa kepala toleh bawah je. Tummy time yg dia ok tu actually bagus sign, means motor development dia jalan, jadi relax dulu jangan push sangat. Kalau you nak try, letak dia sitting position tapi dengan bantal around him untuk support, jangan expect dia maintain posture sendiri pa dulu. Yang penting now is continue tummy time dan play dengan dia on floor, duduk sendiri tu akan datang naturally bila dia ready, usually around 6-7 months plus. Tapi kalau you still risau, better check dengan pediatrician your baby, they can assess kalau ada development concern or not, espeically since premature birth.