Taking out anger on toddler

I’m a mom of an infant and a toddler. Ever since #2 arrived, I have been losing it with my toddler from time to time. I lose my patience and my temper when he does toddler things, like repeatedly not listening or tantrumming. I will work myself up into a rage where I scream at him at the top of my lungs. I thought these incidents were getting less frequent, but today was really bad and I even lightly smacked him on the cheek. I feel SO guilty and I think I need help. Is this postpartum rage/anxiety? Is it just losing patience with having a toddler when I’m already stretched thin with caring for 2 kids since I’m a stay-at-home mom now? I’m scared of admitting I have a problem to my husband/family. I really don’t want to take medication. I’m open to therapy but have no idea where I’d find the time and childcare to make it happen.