How are you taking your gravity readings? If you're using a hydrometer, carry on. If you're using a refractometer, remember that it is not accurate when alcohol is in the solution. There are calculators that you can use to determine the correct gravity reading when alcohol is present, but I find it easier to use a refractometer for OG and a hydrometer for FG. When you are trying to determine if fermentation is complete, I use a refractometer, since it only "wastes" a drop or two of beer. Since I'm only looking for a change in gravity and not the actual reading, this works fine. I take a sample and write down the number. Wait 2-3 days and take another sample and check it again. If the reading changed, then you know something is still happening. Wait another 2-3 days, take another reading and repeat as necessary. I've experienced a wide range in fermentation times depending on the yeast, OG, temperature, etc. Don't assume 2 weeks is always the fermentation time. I'd also recommend calibrating your refractometer regularly. Mine drifts quite a bit in between uses, for some reason.