The amount of sweetness relates to how long it has brewed.  If you brewed it in a cooler area than you normally do, it will be sweeter - will have more sugar in it.  I have let mine brew to the point where it no longer has any sugar and ends up as a vinegar because I'm diabetic.  I always taste tested it for sugar content before using because the length of time it takes to mature differs with the seasons.  So - if you do not want the sweet taste check it before removing the shroom.  The "fizzy" part is a normal part of the process that you probably didn't notice before because you let it brew longer.  Remember too that fermented kombucha contains alcohol and Linsay Lohan claims she failed an alcohol test because she drank kombucha tea.

http://www.huffingtonpost.com/2011/06/24/lindsay-lohan-kombucha-te_n_883724.html

After several months of using kombucha my self I quit making it because I found no benefits and found it to only increase my appetite which is not what I wanted to do while being over weight.