Why does wishing myself happiness in Metta trigger a voice saying I don't deserve it and spike anxiety?

I began Metta meditation since my therapist has recommended that I should be more kind to myself. However, when I repeat words or expressions such as may I be happy to myself, some wild voice comes to my mind and screams right away telling me that I do not deserve it. This inner quarrel is a burst of anxiety and overwhelming guilt since I cannot even create a goodwill with myself. Am I simply deceiving myself, or is this resistance a step that needs to be undertaken in order to get over the self-hatred? My name is Aarav and I was born on 10th February 1996. Time: 9:15 PM. Location: Mumbai.