how did you mix the sugar in prior to bottling?
I ask that too. When that happened to me, I had not mixed my priming sugar well.
I either had really sweet bottles with carbonation, or flat bottles that tasted like the beer did at bottling. Thankfully I didn't get any gushers. You might be careful opening other bottles if you didn't make sure to mix your priming sugar in well.
sigh... 2 weeks is not enough time... let it sit at least 2 more weeks before you crack another one open... if you can muster up the patience, wait 6 more weeks... it will be worth the wait. Porters in my experience take longer to 'mature' when bottled.
Two weeks is about the bare minimum for carbonation, but I find the flavors will develop better if you give it more time.
If this was a kit beer, you didn't follow the instructions that came with it did you?