My 18month old has been waling at 12am every night for 3wks now and shouting for 3hrs. what can i do?

I'm sorry to hear that, it must be very tiresome for you to deal with. My baby of 15 months still wakes in the night at times wanting a feed. I think maybe you should try to play with him and tire him out before he goes to bed, but not too close to bedtime so you dont' excite him too much. It could be that as a boy he has more energy and is therefore more playful. Calm him with a bath, a book read or sing song, and if you already doing all that I can't think of anything else. Maybe speak with a midwive of a paediatrician. Good luck.