Are positions such as joking about the obligation of paying Zakat on sweets, or laughing at a child's mistake regarding the name Khadijah, or joking with "I proposed to you" considered mockery of religion or disbelief?

The inquirer's fear and her intrusive thoughts are conclusive proof that she does not trivialize religion. There is no mockery of religion or its rituals in the situations she mentioned, as mockery is derision and trivialization. The best cure for her condition is to completely disregard these intrusive thoughts.