Like Mystical said - one reason I have problems sometimes is if I'm lazy about the reality checks and do it half heartedly and make excuses for them. Perhaps its the same with you?
For example, the 'block your nose and breathe' RC works very well, but not if you block your nose for only an instant and just say 'Yeah, I couldnt breath... moving on'

Every time you do a reality check - ASSUME you are *dreaming*.... until proven otherwise

And like the others said - everyone is different, and you need to find what RC's work for you
For example... reading is a very bad RC for me personally - because I read fluently in dreams.
However others don't find the same problem as I do, and that RC works just fine
Add another RC or 2 to your list of checks, until you are sure which ones work for you

So as a suggestion and summary:
1) Add perhaps 2 more RC's to your routine - at least until you know which ones work for you. Then you can cut it back to 2.
2) Assume you are dreaming until proven otherwise
3) Never rely on only one RC. If one fails - *always* try the others as well. And don't prejudice the results because of the first RC ... again, still assume you are dreaming until proven.

Good luck