I think he's showing signs of jealousy, which is understandable.
How about a sticker chart? You don't have to explain it all to him first, just wait until he's done a nice thing for the baby (passed you a nappy/given him a kiss etc) and then say "you are being so kind DS, you can have a star on my special chart because you are being so good".
He will then feel proud of himself and you can hand them out for other times of good behaviour. Only praise the positive, so no taking stars away or saying "right, you can't have a star", only positive when he's good.
Also - at almost 3, does he go to preschool? As they can go from 2trs, 6 months, it might be worth (if budget allows) to get him into a local preschool for a couple of sessions a week. That way, he'll be getting rid of his excess energy in a controlled way, learning to share etc and giving you a break whilst you have the baby.
Also - perhaps on the weekend, you could take your son out on your own; he perhaps sees you and the new baby all the time and feels pushed out. It's really important to keep the bond with the first child, even though you are spending so much time with the new baby. If you have a partner, or someone to look after the baby (even if it's only for half an hour), spend some quality time with your son at the park/cafe etc and he'll really appreciate it I know.
Hope this helps 