DS turns 3 in a week. The past week has been like a complete personality transformation - and not for the better 
DS used to be a really kind and 'sensitive' boy but is now being quite unpleasant. He has started spitting in defiance. Started using his considerable physical strength to pull/push me and DH. He has broken some Christmas toys already with no hint of remorse. He has started SCREAMING at full volume if things don't go his way - I mean, we've obviously had tantrums before but he's been easy to talk round and reason with. This screaming is unreal though!
It seems like naughty step, stern voice, all the usual suspects aren't having any effect and he just laughs in our faces.
Is this a common phase? He has had a bit of a cold and does suffer with severe glue ear but tells me his ears don't hurt so I'm not inclined to think its illness.
Any ideas on discipline techniques? I've tried ignoring bad and specifically praising good but I feel it's not doing anything and there is some bad behaviour - like the spitting, that I can't ignore?