carbonation question

After a solid carbonation my beers always have an excellent taste, I understand to be patient and good things will come.

I just would like to better understand one thing.
I have recently made a stout which tasted absolutely fantastic pre-carbed.
As well as one I tried one week in.

However this week (2nd week) I decided to give another taste to see how its coming along, and it was borderline awful.

Knowing I still have another 2 weeks or so before the finished product,
I was wondering why the major taste drop

Take a look at the hundreds of threads that ask this exact question and you'll see the exact same answer with timeframes depending on the beer. For most beers, where you're waiting 3 weeks:

When you add the priming sugar, the yeast will start eating it and produce alcohol, co2 as well as some byproducts. (esthers and whatnot) This is like it's doing the entire regular fermentation process again (some yeast reproduction). So what you're tasting would be what people call 'green beer' too young.

By the second week, some to most of that tends to be cleaned up, since the yeast consumes some of those byproducts, but the beer won't be fully carbonated and a lot of the pressure will be in the airspace.

Finally, by the third week, the co2 seems to equalize between the headspace and the beer, giving you a carbonated beer.

When you're looking at high gravity beers, like a stout, that time is spread out a bit longer. Chances are, you're just tasting green beer. Alternatively, it could be infected with something which creates the offtastes.

This is why people keep stressing patience, and this is why us new brewers tend to be curious to find out why we have to be patient. It's also why some of us decide to keg, so we don't have to wait as long for carbonation, since the beer won't have as long of a wait time.

+1 KevinM

If you don't mind spending a few bucks you can always get a CO2 setup and force carb the beer, you'll run less in to the problems of "green beer", but even then you still need to wait to make sure your beer is fully carbed prior to drinking.

Kevin's pretty much right. The yeast is "fermenting" the priming sugar, and consequently the yeast are producing some byproducts of fermentation, the same stuff that leads to off flavors, when they're done with the work, they will go back and clean up those byproducts as part of the bottle conditioning process. So it's natural for there to be a "dip" in the flavor profile. But if we just walk away from the beer during this period and not waste them by constantly tasting them, then we'd never encounter this, nor would we care because the beer will be drinkable.