My family used to love watching “Extreme Makeover: Home Edition,” but we stopped because almost every member of every family (who was given a newly-built, custom-designed home) could not express themselves without saying over and over, “Oh, my God! Oh, my God!” That seems to be the favorite exclamation today of “religious” and “non-religious” people alike. 
The name of God is holy (Psa. 111:9) and not some expletive to be thrown around! If you’re just determined to say, “Oh, my God,” then use it the way it is used in Scripture (as a proclamation of a humble and submissive heart). “OMG, I am too ashamed and humiliated to lift up my face to You” (Ezra 9:6). “Remember me, OMG, for good” (Neh. 13:14, 22, 31). “Save me, OMG” (Psa. 3:7). “OMG, I trust in You” (Psa. 25:2). “OMG, be not far from me” (Psa. 38:21). “I delight to do Your will, OMG” (Psa. 40:8). “OMG, make haste to help me” (Psa. 71:12). “I will praise You and Your faithfulness, OMG” (Psa. 71:22). “OMG, incline Your ear and hear” (Dan. 9:18). No, never as an expletive! But, always as exaltation!