21 weeks pregnant

Last night I started having really bad and scary thoughts of me hurting my 2 year old son. I’m 21 weeks pregnant and this has never ever happened before. I would never hurt him but I don’t like these thoughts. I’m also just really sad too. I called my ob to see if she can get me in to talk but I’m wondering if this is normal? I feel evil almost and I can’t stop these unwanted thoughts and sadness.