Step parenting

I feel like lately I'm on the losing end of every battle. Granted I'm pregnant and my emotions and a little wakey. For a while now my step son hasn't been eating what's made for dinner so his dad haggles with him (he's 5) so if he eats X amount of food he gets to have whatever snack he wants like an hour after dinner. Tonight after I made dinner he opted for getting him a happy meal and when he was done he was still hungry so I made him some or our left overs and all hell broke lose. He is just going crazy lately because he gets 7 warnings before a punishment is put in place. Its so exhausting because I'm wasting my breath and I feel like my word has no value.