Its technically possible to fend off strep throat without a doctor or medicine. If the immune system is properly equipped to deal with it, it will eventually fight off strep.
However, its also technically possible for the immune system to fight off the bubonic plague and measles, and yet only a complete moron or ignoramus wouldn't get vaccinated against measles and go to a hospital to get their strange pains, bumps, etc, looked at. You also don't get to find out if the immune system can fight off the infection on its own until it does exactly that or you die. And there's no cure for death.
And how it fights it off might cause problems down the line. You want to know how the Bubonic plague didn't kill everybody in Europe but seemed to have a liking for young non-Jewish men in their prime? Iron in the blood. Plague bacteria requires iron for strength and efficacy, as well as iron-rich macrophages to spread the plague bacteria around through the lymph nodes, and it gets it from your bloodstream. Denying this bacteria sufficient iron will eventually starve it to death. For women, breastfeeding and menstruation healthily expunges a ton of excess iron from the blood. Children also don't eat as much and have smaller bodies, so they get rid of excess iron quicker than adults. Cultural groups that do not consume large amounts of iron-rich foods, in Europe's case the Jewish population, likewise have less excess iron to get rid of and so get rid of it quicker. But if you're an adult male in a cultural group with a diet rich in iron, you were likely fucked as you are statistically larger than women and children, do not menstruate or breastfeed, and eat a lot of iron. Excess iron thus tended to stick around for a long period of time in your blood, it took longer to get out, and the plague bacteria doesn't just survive but outright thrives as a result. That is, of course, unless you had hemochromatosis. Hemochromatosis is when your body doesn't know when to stop sending iron to its organs, leading to an overdose within decades if not treated. However, this has the side benefit of leaving less iron for harmful bacteria like the plague to feed on in the bloodstreamf. The less iron in the blood, the quicker the bacteria starve to death (Your body does have some instinctual awareness of this-- it automatically packs away iron away in organs when it detects an invader-- but it is often not enough as plague bacteria can infect the iron carriers to get into all kinds of areas and it takes time). Most adult men thus had to have some variant of hemochromatosis to survive, and even women and children could benefit from its plague resisting abilities. Now the plague is extinct, enough European people survived to rebuild society in that region, but hemochromatosis patients and carriers are still remarkably common in Western European people (particularly men) and now doing more harm than good because if not caught and treated with bloodletting, hemochromatosis will kill people in their 40s or 50s.
If you can avoid the human species having to evolve a genetic disorder to survive certain illnesses, you should do so. So go to the doctor and comply with the treatment-- enough people doing this will prevent nature from stepping in and using its own, likely full of collateral damage that long outlasts the problem it was trying to address, solution.
Don't risk death because of fear. Prevent humanity from evolving higher rates of genetic disease. Go to the doctor and follow the prescribed treatment within reason.
