yes, thrush getting more prominent can be a sign of die off.
it can also be a sign of yeast growing, but if you are following a strict low carb diet, with almost no Sugar (except maybe granny smiths) you can be sure that the increase is die off.
my tongue gets much more coated when i have die off, i am sure this is the case, keep doing what you are doing.
you may want to check out "oil pulling" for your gums and teeth. there is a forum on curezone and it seems to be very successful for some people.
your probiotics are fine. FOS are neccissary, they are often called "prebiotics" and without them your "probiotics" are almost useless.this is what you can do to make your probiotics work better. get some good prebiotics, or make sure you eat plenty of prebiotics, more than are in your pills. to make sure you are making progress you may also consider taking an antifungal such as caprylic or undecenoic acid with meals, and taking your probiotics with prebiotics between meals on a somewhat empty stomach (some people will not reccomend on and empty stomach, but with the prebiotics it is better than taking them with a meal when they often get digested.)
prebiotics canb be soluble fiber such as inulin, special sugars such as FOS or xylitol, and pectin, are neccissary for good bacteria to flourish and make colonies, it feeds them and helps them stick to the walls of our digestive system. these things are found in plenty in raw vegetables and fruits, and beans have particularly high fiber. without eating these things our flora gets messed up. and without eating them it cannot get better.
any Sugar that is from your probiotic supplement is neglegent when we are talking about feeding yeast. focus on the foods you eat, and avoiding things that you may be sensitive to like vinegar, citric acid , wheat, pasteurised dairy, any sugar. for me it would include: carrots, onions, cheese, peanuts, other nuts
good luck, youre on your way, hang in there and it will get better.