Sounds like malabsorption, acidosis, with adrenal exhaustion.
There are a couple of options, but a acid tongue pH means low enzymes, the body will not function properly.
Once the pH goes out of wack, ROS sets in, systems start to malfunction, Bacterial balance goes out, Minerals and metals get lost, health declines. Magnesium, Potassium, and Calcium are lost.
Without a gut bacterial biodome lipids, oils, and essential fats are not absorbed properly, leading to even more acid.
Toxins can backup causing distorted system functions, The body will make it a priority to get essential elements first, and ignore longer term processes. After a while the junk piles up.
Ultimately the body looses enzymes which are part of the regulation loop of the key digestion processes. Usually there are signs of poor digestion, odor, gas, pains, undigested foods, leading towards malabsorption.
I suggest a hair analysis to evaluate your system status.
Cannot tell if this is a acidifying process, or the downward spiral of acidosis.
If there is an underlying infection, it certainly is secondary to low bacteria, acid, and poor enzyme protein absorption. Protozoans are known to infect the GI tract, and cause oil to float on the top of the water in the toilet bowl.