The Spawn!

I am struggling with holding the power with my 3 year old son. He yells at me, hits me, throws stuff, etc. I feel like I have no control over my son. Frustration is beginning to take over. I know its the age but it gets a little much. Am I a bad mom for not having control? He tells me no. He is the kid you see in Wal Mart and swear your kids will never act that way. Its not always that bad but Monday, we went to walmart and I left before I even began shopping. I was the mom you look at and wonder how she can lose patience with a little kid. Now I know how. Gosh its so embarassing. Any advice? I love him so much and I don't want this post to come across wrong but my goodness its been hard lately.