So I wrote down my dream and It was all about lucid dreaming. I plugged my nose and tried to breath like 20 times in the dream, and I tried to fly and it didn’t work so I continued on. When I do reality check when I’m awake, I think that can be dreaming. Why isn’t it working? 
well if you tried to fly, then you were probably a low level of lucid? also try doing other RC’s. my regular RC is just looking around for anything curious, then looking at my hands, then pinching myself while thinking ‘if this is a dream, i wont feel anything’, then i try to put on hand through the other whilst thinking the same thing. and finally recalling where ive come from and what im going to do next
In order for RCs to work in a dream, you have to believe it will ‘fail’ proving that you are dreaming. If you’ve visualized the RC failing and truly believe it will fail and still you can’t breath through your nose/push your finger through your hand etc. then try a different RC. Some might work better for you than others. Good luck, and happy LD 
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I find that reality checks in my dream fail when I already know I’m dreaming or I have a very low level of lucidity.
I’ve used nearly all of the common ones listed, but remember reality checks are just things to prove your not experiencing reality, it can be something as simple as a box missing inside of your room, or a letter/word being unclear. In your dream they are all around you, you just need to find them =]