JEALOUS

Just a background first. I have a son that will be 5 in two weeks and a little girl that is 8 months. We got lucky when she was born we didn't have any jealousy issues, But lately we have noticed that he has been taking toys away from her, talking back alot more, and throwing alot more fits. He just started throwing fits and talking back when I was pregnant but its getting alot worse. When the baby is sleeping we play games and stuff with just him and even when she is awake we arent just with the baby because she doesnt like to be held so she is down on the floor playing 75% of the time. I am not sure how to handle it. I feel like all I say to him is give her her toy back, stop it, dont do that. I am not one to yell at him or spank him. I do use time out but it doesnt seem to work anymore. He was cry and go sit in there but it doesnt seem to do any good. I am one of the people that want to be as positive as possible because we are showing out children how to behave but on the other hand I dont want him disrespecting us or being mean. oh and the toy issue he was a million and one toys but he uses hers which is find I let him play with her toys as long as she doesnt have it in her hand. We just dont know how to handle it anymore. Etc... we were at a birthday a couple weeks ago and they had apool but I had just had my wisdom teeth out and we told him before going that we were not going swimming today (oh and he has a pool at home) because mommy didnt feel good so we werent staying that long. Well when it was time to go he throw the BIGGEST fit ever. I mean through himself on the ground kicking and screaming in the middle of hte party. Yelling he wanted to go swimming. One parent even said well why dont you just let him go. My thoughts were NO if he wants to act like that he is FORSURE not going swimming now. We took him home and we had to carry an almost 5 year out of the party screaming...so we look like horrible parents....any advice.