I wouldn't have expected such a rise in you B/G from 8.6 to 11.2 in 30 mins with just the one cup of unsweetend tea, though you should be aware that MILK does contain both Carbohydrates as well as a simple sugar in its composition, though I would have thought in such a small amount that would not have given you such a rise.
You may need to do some more 'detective' work on yourself to eliminate both the Milk and artificial sweetner, bearing in mind that the human body will be constantly changing, so B/G levels will never stay at the same level for more than a couple of minutes. Most probably the high rise in you B/G is being caused by the MILK, but you may also find that you may be intolerant to the type of sweetner that you are currently using, and changing over to an alternative brand is the answer if the MILK dosn't conclusively prove to be the problem.