That's cause it is! What's the temperature like where your fermenter is? I brewed an IPA this summer and my basement was 61 degrees which was the lower end of the yeast's range. I got slow bubbling for a good 2 weeks then the last week it was SUPER slow but still apparent bubbling for another 2 weeks (1 ever 30-120 seconds). Finally I'd say after a good 4 weeks it stopped and I did my gravity reading. 1.071 down to 1.020. Not the best and could have gone a bit more but after several more weeks it stayed there and it was the best damn beer I've had! It literally vanished from my fridge once others had tried some.
A lot of people (myself included) prefer to the cooler, low/slow fermentation of ales. I for one wish I could but I don't live in that house with the basement 10 out of 12 months a year so I am limited to my apartment.
This will not affect carbonation since you do not have the beer sealed and the CO2 is just leaving the airlock.
Unless you see yickies growing on the top that is not yeast or anything, you are fine!