I have this same issue now with a Scottish ale I brewed and is now just over 2 weeks in the bottle with very little carbonation. I cold crashed it to clear it up then let it come to room temp before adding priming sugar and bottling. Pretty sure the cold crash is the biggest cause for the slow carbonation. This is only my second brew so I guess you live and learn. I'll try it again after 2 more weeks. as a side note this beer has a pretty high ABV at 7.8%, not sure if that affects the yeast or not.