What is making me like this?

I am with my fiancee for the last three years and we had a baby ten months ago and I couldnt be happier but since then we dont have sex as much as we used to we are lucky to have sex twice a month but anyway she is always shouting at our son when he crys and I start to get real mad at her for doing it I start to shout at her and then we fight but that is when I get real mad I start to kick and fling things around the room the other night I smashed a glass bottle off the ground and put glass flying all over the place and I do that a lot I dont know how she is still with me over this and when it happens she says we are finished and I cant live without her or my son so I patch things up with her till it happens again but if it happens again I dont think that it will be fixed and I hate myself for this and I dont like been like this I dont know what to do can you please give me some advice I was thinking of going to a doctor over it like what could be causing me to go on like this I know that I need he

it sounds like you might have anger management problems. if you don't get help soon you might end up hurting someone more than emotionally. they will show you how to control your anger in a manner that is acceptable and show you how to deal with your problems before they get out of hand.
Let her know that you want to get help and that you want to change your temper, she will be more than willing to help you get help. She might even calm down a little bit to help you out.

Smashing a glass bottle because you are angry is not okay. It does sound like you might have Anger Management issues, it's more common than most people think (my brother sometimes has anger problems). If you want to save your relationship with your fiance, you need to tell her that being mad at your son makes you angry and that you may have anger issues but you are willing to seek help and try and control them. And then follow that up by actually seeking help for your anger. After all, think of this - what sort of example are you setting for your son if you're throwing objects like glass bottles around the room just because you're angry? Will he grow up to think that sort of thing is acceptable if you keep doing it?