Is it permissible for me to say, "O my God?"

Allah, the Exalted, is the True God. Whoever supplicates to their Lord supplicates to Him by His Most Beautiful Names and His Sublime Attributes, such as: "O Lord" and "O my God." This is among the greatest ways a servant can supplicate to their Lord, as Allah says: ﴿And to Allah belong the best names, so invoke Him by them﴾ [Al-A'raf: 180]. The Prophet, peace and blessings be upon him, used to supplicate: "O Allah, to You belongs all praise, You are the Lord of the heavens and the earth... You are my God, I have no god besides You."