Welcome tscan. Did hyou know that in the first couple of weeks of dieting that you flush out a chemical that helps you process carbs, this chemical holds a lot of water which is obviously quite heavy - hence why dieters always loose well in the first few weeks and then plateau out before they actually loose 'fat' in the following weeks?
I know I have seen an artical on here about it and on the weight watchers site so have a look - if I can find the articles I will post a link.
So my advice is to just keep at it - get a diet that you can stick with and then go with it for a few months. I think an actual 'stall' in weight loss is when you don't lose any weight for a lot longer than a few weeks.
Hope that helps! I was just like you, would start a diet and see an improvement in weeks 1 and 2 and then nothing weeks 3 and 4 so I would get dishearted and give up but I have lost 10lbs using fitday so far.
Soon to be 133lb