Once a year I bleach my front teeth with “Crest Whitestrips Supreme” (14% Hydrogen peroxide)

Recently, about 2 weeks ago I began to start my annual 3 week course of whitening.
At first it seemed to be oxidising the stains rather quickly and after 5 days I noticed a significant improvement.

Then, I read on the net that also using 3% Hydrogen Peroxide mouthwash can help.
I used it a few times but then I stopped because it seemed like my teeth had reverted back to how they appeared at the start of the process, i.e stained and slightly yellowish.

Anyways, I disposed the bottles of Hydrogen Peroxide solution and I am going to continue with the Crest Whitestrips.
I was wondering, what may of happened? Why did my teeth look significantly whiter and then suddenly revert back to a stained appearance?
Did the Hydrogen Peroxide solution cause this?

I tend to stay away from acidic drinks and I am a non drinker and non smoker, I use Sensodyne Pronamel toothpaste & Mouthwash.
However, I did drink a few pints of pure orange last week and I wondered if the the peroxide had made them more porous to stains?
Also, is it okay to use mouthwash right after bleaching?

Any help/advice is appreciated.

Thanks in advanced