My 4 y/o is overwhelming me

I have no patience for my 4 y/o son right now. Don't get me wrong I love him to pieces but he's just been getting under my skin lately. He's always so hyper and never listens to me. I'd like to think I'm good at disciplining him with spankings and time out. But he just doesn't listen and he cries and whines for EVERYTHING. I feel like I'm about to lose my mind with him!! Then to think I'll be bringing a new born into our home in a few weeks is just overwhelming me. Any tips to help cope with this or to help with my son?