Most likely you're making beer. You might have a leak -- the screw cap probably. If you loosen the cap slightly and you don't hear gas escape, then you can believe its a leak. The bubbling tells you the yeast are making beer and CO2.
I'd recommend that you DON'T take the cap all the way off. Let the beer ferment out (maybe two weeks or three if you can wait) then bottle condition the beer.
Good luck.