Losing it

Please don't judge. I know I am wrong that is why I am asking for advice.

I am 31 +4 with my 3rd. I have two toddlers whom are only a year apart. Lately I have been easily losing my temper with my kids and I can't stop. My daughter LOVES to scream back at us when we tell her to do or not do something or if not she will throw a tantrum if things don't go her way. Also her favorite word is no. My son LOVES to cry and whine for EVERYTHING. I mean everything. He will even cry if someone gets to close to him. Earlier he was crying because a little girl was looking at him. He also cries if he doesn't get his way or he will hit/throw himself on the floor. All of these things set me off and I can't stand it. I love my children more than life itself but they really know what buttons to push. I hate the way I have been acting and I know that maybe it is my fault that they are behaving this way but tbh I am at a loss on what to do with my children and myself. To add to the cake I'm having another baby and I am terrified of her. I love her already but I am so worried she will behave the same way as her siblings. Please give me advice on what you think I should do? I just want to be a better mom for my kids and I really want to be calmer and more at peace. What do you recommend I do?