the big bubbles are not from your carbonation levels, they are most likely from the body of your beer. This is typical of "can only" brews (I'm assuming you are only using a kit can and a kilo of dextrose/sugar?). To get a tighter head on your beer and better mouthfeel, try adding a kilo of malt extract in place of your dextrose/sugar and try steeping some specialty grains, such as crystal malt and carapils. You'll get better flavoured beer and it's the first step to getting the confidence to try formulating your own recipes and getting away from the "kit n kilo" approach.
Cheers - Snow