Llis, it would appear to me that your first shot, ie with No Flash, is a little under exposed, hence the dark. The one with Flash is rather burnt out owing to the flash being a little bright for the distance you are from the camera. In the first instance, either increase the exposure or is there some way in which you can reflect some of the light on to yourself as the background would appear to be adequately exposed. ie. a strategically placed piece of white card.
When using the flash at this close distance, if you cannot adjust the flash output then a piece of tissue ie. toilet roll, placed over the flash or held in front of it, should do the trick. It may require more than one thickness of tissue. Trial and error is about the only way of getting this right.
When you save a photo to put it on the net, ie WC! you will have saved as a jpg. This is what's known as a Lossie file format ie. it makes the file size considerably smaller but with loss of detail. The more you compress the file, ie the smaller you make it, the greater the loss. I see that you reduced your picture down to 15 KB giving a considerable loss of detail and sharpness. As you will know WC allows a file size of 150 KB and the closer you come to this size the more detail you will keep. Having said this, most cameras store the pictures as jpg which means you have lost a little detail to start with and will then lose more when saving for the net as previously mentioned. So I think you will find that even when we manage a file size of between 100 and 150 KB most of us use a little sharpenning before posting.
I am including my version of your dark picture, having played with it a little in Corel PhotoPaint. The results are still below par - mainly, I think, because you had saved to such a very low file size. Unfortunately, once you have done so and lost detail there is no way to regain it.
Hope this is of some help.