Edit: thank you all very much for your time, thoughts and effort to reply to this. I really appreciate it and I try to find a new doctor.
Your questions and encouragement were very helpful and made me realise that my symptoms are too strong, considering my lifestyle. For those who asked questions, here are the answers:
I eat healthy, we cook fresh, colourful food almost every day, only drink water, coffee, tea, no alcohol, no smoking, no fast food.
I walk my dog several times a day and when I'm doing something where I have to sit for an extended period of time, I take a little walk evey hour or so and also use a standing desk attachment to change my position. I sleep on a really good mattress (my partner struggled with our last one so we invested in a good pair of matresses, matching our body type)
I have a healthy weight on the lower end of the scale. I had to cut back my exercise that I was doing for twelve years due to the pain, switched to light Yoga and streching until even that became unbearable.
Thinking about all this together, I think my fear of not being taken serious made me believing my current GP.
I'm in my mid twenties. My body seems struggling, since May/ June, so some time then I went to my GP. His response: "everyone experiences symptoms of their ageing body at a different time, seems like you just experience it earlier..." This was around May/ June, it just tends to get worse. Which leads to the questions featured in the title. My body hurts, like, a lot. Especially my low back/ sacrum. My knees, shoulders, wrists, ankels. My hands are swollen in the morning and they hurt, I can't unscrew any lids or bottle caps, sometimes can't even write anymore as my fingers are very stiff. As the rest of my body. I can't reach for anything on the ground in the morning, it makes everything so difficult. I can't really bend over to tie my shoes or pick something up. I can't do my regular activities even though I really want to do my sports like climbing which I really like. I do like being active and want to stay fit. But it just hurts too much. At the same time, resting somehow makes it even worse. I'm exhausted, but need to constantly move around on a low level. How is everyone else doing this if this is what ageing feels like? How am I supposed to have kids or even just live like this, as I always just hear that with an ageing body, everything just gets harder every year? I really do appreciate everyone who reads this. Thank you in advance for answering if you have any tips on how you manage this
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.