A new sibling is a very hard thing for many young DC to accept and adapt to. Is this behaviour really only since his sister was born? If so, I'd take a deep breath and just continue with what you're doing - setting boundaries, not accepting bad behaviour, consistent and firm reinforcement of boundaries, etc. If he doesn't already go to nursery or play group it may be time to enrol him and give him some time with other DC his age. It will give you some breathing space too.
He wont stop talking, from 5am - 8pm and it's killing us. He is very boisterous - but this can manifest as hitting, kicking & head butting (mainly me, but this has been constant)
He sits in time out, but just then caters on regardless and in the main doesn't do anything he's told. He's started been more aggressive to other kids & threw something at an adult this week - totally unprovoked.
Really it boils down to this - I fear he's become spolit, he's incredibly hard work - DH & I have both cried in last few weeks as it's taking toll and we just want him to be... I don't know easier? Are we just deluded?