mashy/kwan,
dun worry, it takes time and when the child is ready, who knows he may just go to the toilet and do it there. I heard that boys are slower to train than girls. I intro the habit of going to toilet by telling him how wonderful it is to flush the toilet after use, keep broaching on the topic for a few days then one day just ask whether he wants to pee in the toilet just like daddy and then flush the toilet. He likes to flush more than pee so we told him that he could only flush when he pee/poo, otherwise no job for Mr toilet bowl to work on. Another factor could be that my son plays with my nephews once a week, and both of them are older and toilet-trained. Son always says that he wants to be like korkor wear briefs, but I told him can only do so when he knows how to control his bladder. For us, toilet-training takes 2-3weeks before it becomes quite accident-free. for poo, we would "ngggg" him at the toilet bowl with child seat after breakfast to let him get use to a routine. Once he got the routine, and can feel the urge to poopoo, he would tell us. But one problem with him is that he's very fussy with toilet, if we go out to hawker centre/coffeeshop, he die die don't want to use the toilet, so we got to grab him and run to find a clean toilet when he tells us that he want to pee/poo.
Kwan, maybe u can let him wear brief for a short period of training time per day when he's more alert and less cranky. if you keep putting on diaper, he knows that there's diaper so he won't tell u or make it an effort to tell you when he got to urge to pee. Having said that, the first few times sure would be messy and expect accidents, so put him on floor to play instead of bed/sofa.
Good luck in training!