Hey folks interested in curing angular cheilitis. I've just gone through most of the thread and there is some good advise, but the primary issue causing this is still missing, so follow along:
First, you may want to rule out a vitamin B deficiency--especially B-12 (more likely if you're a vegetarian), sometimes B-2, and iron deficiency anemia can be causative too (more common in non-red meat eaters). While these types of nutritional deficiencies can be your root problem, typically these aren't.
That said, it is most likely that your angular cheilitis (AC), or sometimes called angular stomatis (AS) is causes by a fungal infection called Candida. While Candida sp. are normally present in the human body, there is a system of checks and balances which naturally keep them in check. E.g. healthy bacteria such as probiotics help with this. Any time you go on a cycle of Antibiotics you "healthy" bacteria population takes a tremendous hit which then allows the Candida to increase in numbers, especially if you're feeding them the standard American diet (SAD) which is heavy in starches (bread, pasta, potatoes, cereal grains) and sugars of all kinds. Candida feeds on sugars such as glucose, (what are the typical sources of glucose? All starches and sugars. Yes, starches too b/c they are just long chains of glucose molecules which are broken down into their individual glucose molecules before they can pass from the small intestine into the blood for use by the body.
Anytime that you have high blood glucose levels, especially chronically as with diabetes or pre-diabetes, your glucose levels are going to be elevated and this isn't only your blood, but also your saliva too. Read this again, b/c with elevated saliva glucose you're feeding the Candida in your mouth.
Another very common was people harbor oral Candida is if you wear an oral denture and are not disinfecting it with a bleach/water solution daily. The denture material is actually a wonderful microscopically porous material that not only is a great harbor for bacteria, but most especially fungus b/c of the xenoestrogens that are a component of the resin matrix. Candida love estrogen--one reason why women on estrogen replacement have such high rates of vaginal and other fungal infections. If you have oral dentures most of the available cleaners do not kill the Candida, to effectively do that you need to soak them daily in a cleaner that contains sodium hypochorite (also know as regular bleach)--just be sure and wash thoroughly before wearing again. Also, regular baking soda works wonders to kill off Candida and takes away odors, so consider alternating these two as your regular cleaner.
AC is caused by Candida--if the open cracks develop a viral/bacterial infection, it is secondary to the Candida.
It is possible to only have oral thrush, but much more likely it is systemic and moving up your esophagus while you sleep (typically we don't swallow too often in our sleep where swallowing would otherwise keep most of the Candida in our lower GI tract,rather than in our mouths) in the horizontal position. Save yourself the doctors visit and do the simple home test: before bed put out a clear glass filled with water. Immediately upon waking, gently scrape your mouth (mostly tongue) with a spoon and/or just swish the spit around in your mouth as best as you can and then deposit it in the glass of water. Without disturbing the glass, let it sit for 15-30 minutes and hold it up to a light to look at what happened to your spit. If it's still floating in a semi-solid mass with no little round masses (spores) or very fine threadlike projections exiting the spit mass downward like tiny balls or jellyfish tentacles (fungal hyphae)(Candida is dimorphic--that is a two form shape shifter) your probably not harboring Candida; however, if you see either of the above, you need to treat the Candida for long-term relief--not just the symptomatic cracks at the corner of your mouth.
I'll follow this up with more later, but for now, I'm assuming that everyone here is partaking in their own health care, rather than leaving it all to a doctors guidance, which is the first step . . .