I get something similar after a few days.
Is your tongue looking like it has some wet whitish fur on it? If so, it’s stuff that’s detoxing through your mouth (because the mucosa is thin there), and I remove it through oil pulling; that usually helps with the bad-taste problem.
Here’s how to do oil pulling: take about a spoonful of oil (I use coconut oil, but you can use sesame oil or really any healthy, pure oil). Put in it your mouth, but don’t swallow. just swish the oil inside your mouth for a good 15-20 minutes, then spit it out. The oil should be thinner and whiter when you spit it out.
It helps to remove fat-soluble toxic elements. In Ayurveda I think you’re supposed to do oil pulling like once a week. When I’m fasting and I get the white-fur-bad-taste thing, I’ll do it every day. It doesn’t have any side effects and it’s not dangerous.