Agree with everyone else that this isn’t normal for someone your age and get a second opinion.
However addressing your other questions: you’re at an age where lifestyle starts to really matter. Diet, exercise, ergonomics, environmental exposure to pollution/toxins, alcohol/drug use, sleep habits: these are all things that many healthy young adults can avoid having to worry about… until suddenly they can’t anymore. It is common, especially starting around age 30, to find there’s unhealthy behaviors from your teens and 20s that you just can’t do or do to excess anymore. It’s different for everyone; for some people it’s that they can’t sleep on a crappy mattress anymore, or drink certain types of liquor, or pull all nighters, or eat garbage, etc etc.
So while it sounds like you have some personal health issues outside of what’s “normal,” you still are at an age where the cumulative effects of a poor lifestyle can start to catch up to you. I think a lot of people greatly underestimate how sedentary their lifestyles are in particular, and of all the behaviors to change for the better as you age, going from sedentary to active is probably the hardest, given that our world is built to keep us sitting: sitting in our cars, sitting at our desks, sitting on our couches, basically sitting from the moment we wake until we go to sleep. Humans never lived like this until very recently: basically every decade since the personal automobile became the standard mode of transportation it’s steadily gotten worse. So yes, definitely do some doctor shopping, but now is also a great age to take stock in your lifestyle and how you’re treating your body. Because yes, it does get a little harder each year, but the speed of which it gets harder is at least partially up to you.