Based on what I've seen and read, I think that you may not be attaining lucidity, possibly due to not lingering on the question 'am I dreaming?' enough to get that realization. Because dreams are unconscious until lucidity is gained, you have very little control over what you think until that point, so it would probably take a good bit of focus to become sure that you are dreaming. Personally, when I do reality checks, I linger on the question for about one minute. I also think that doing different reality checks could help keep your subconscious from getting used to the same reality check, and would make failed reality checks less common. These seem to be some of the most effective pieces of advice that I have found.