Whenever I realise I am dreaming, I say to myself "this is a dream" so I can fully realise I am dreaming, and take advantage of my new-found situation. However, whenever I say "I am dreaming" (or something along those lines) / realise I am dreaming, I can feel myself being pulled out of the dream and waking up. The only way I have found to combat this by saying "I am not dreaming" which invariably ends up with me losing lucidity, putting me back at square one.
Any advice on how to stop this? I have read that just going about your business as you were before you realised you were dreaming helps, but what is the point in that? You might as well not have even become lucid in the first place.
I have also heard many people saying that this problem can be due to over excitement, yet whenever it occurs I treat the situation like I have been there a thousand times before, keeping over-excitement to a minimum.

I would be extremely grateful towards anyone who may have an answer to my very annoying problem thanks.