Why are my potatoes sour?
Remember that the potato is a member of the nightshade plant and you can use a potato as a battery. Better even if cooked. What you are tasting is basically the solanine (which often has a battery taste...I believe there is a correlation there somewhere but it could help people remember not to eat bitter potatoes). I've tasted it too but not everyone has the same taste buds as we do. 

Also, the battery (essentially the life of a plant) that I'm referring to starts when the sun comes into through the leaves (Solanum tu-berosum) and producing the starch, "which is transferred through the plant to its underground stems, known as stolons. Starch collects at the end of the stolons, forming swollen sections called tubers. These are the potatoes." Just like any living plant, the tuber stores energy for the plant. "The complex process of turning sunlight into food energy is called photosynthesis. ... The potato plant can live for six months without the energy of the sun, because it survives on its stored chemical energy in the form of starch in tubes, or small sacks called tubers."...(http://www.simpsonstreetfreepress.org/science/plants-and-photosynthesis)

When your potatoes sprout during storage, they’re using available light and stored starch". During harvest and storage, "When exposed to light, potatoes manufacture increasing amounts of chlorophyll as well as two bitter-tasting alkaloid compounds, solanine and chaconine" especially prolonged exposure to light with improper handling and storage. "In high concentrations, these can not only make potatoes taste bitter but also can cause headaches and stomachaches" (among other things). "A 4-ounce (114 gram) potato naturally contains 5 to 6 milligrams of solanine and chaconine, which is considered harmless. But when a potato looks green from an increase in chlorophyll, it indicates that it will also have higher levels of these alkaloids-  as much as 20 times in potatoes that have turned completely green." I have read here that you can "deeply cut away any green parts" (...https://www.finecooking.com/article/the-science-of-cooking-potatoes-2);but I have also read conflicting information asking to avoid them altogether. I already do not eat potatoes when dining out including fries but I also avoid eating potatoes within a couple of days from each other. According to the Smithsonian... (https://www.smithsonianmag.com/arts-culture/horrific-tales-of-potatoes-that-caused-mass-sickness-and-even-death-3162870/); "A general rule for avoiding illnesses like the ones described above? Green and sprouted? Throw it out." On the site, the Smithsonian will give you many links that I've found interesting. Where I live, the potatoes are mostly green and I plan cooking potatoes when I see good ones on the shelf. We have a small offshoot grocery from a big named chain so we get all of the bad stuff here. I makes me sick every time I see them selling otherwise discarded produce to uneducated victoms.

I'm glad you are ok now.

..."A 4-ounce (114 gram) potato naturally contains 5 to 6 milligrams of solanine and chaconine, which is considered harmless. But when a potato looks green from an increase in chlorophyll, it indicates that it will also have higher levels of these alkaloids-  as much as 20 times in potatoes"...

Here is a link with more information: 
https://www.finecooking.com/article/the-science-of-cooking-potatoes-2 and check out an unbiased article on Mother Earth News at https://www.motherearthnews.com/organic-gardening/green-potato-myths-and-safe-potato-eating-zbcz1509

Here is a very scary place to research. It may make you never want to eat potatoes nor any nightshade ever again. https://sciencebasedmedicine.org/killer-tomatoes-and-poisonous-potatoes/

As we know, our diets are lacking and research is all over the charts but until our governments step in and investigate the money hungry monopolizing industries; it is to each his own so research and research again but it is always a good idea to not rely on only one source of information.