OMG! Sissy, you could have written my history!
1. You are not a hypochondriac! Don't let ANYONE gas-light you (tell you that nothing is wrong with you). This makes me so angry on your behalf.

Specialist doctors, in my experience, prefer to keep things simple for themselves by only focusing on their body part without considering the entire picture of your body.
And that's how they often miss systemic problems.

2. I am not a doctor, but it sounds to me like you might have an autoimmune disease or multiple autoimmune diseases.
Have you had any blood work done?
The first step blood work for autoimmune disease is called ANA for antinuclear antibodies. Your primary care doctor can order this test for you.
A negative (normal) result doesn't mean that nothing is wrong with you.
A positive result will make the doctors pay attention to your case and remove the hypochondriac obstacle.
A rheumatologist diagnoses and treats autoimmune diseases.
3. I have some more ideas for you, but my eyes are starting to bother me. I'm going to try to get all of my ideas written. Forgive me for being abrupt and perhaps harsh. Sorry about typos.

If you haven't done so already, make a written/typed list (it impresses doctors) of your symptoms, inluding how they impact your daily living and include the pain level on a scale of 1 to 10, with 10 being blinding pain.
Group your symptoms by system: all joint and muscular together, for example. Include start dates/year/age--For example- my hip pain started when I was 20 years old.
Put the worst/most intrusive/most painful group first on your list.

At your next doctor's appointment-- at all of them-- have 2 copies of your list. Keep one list for yourself and write notes about what doctor says on it. Give the other list to the doctor, and ask him to read it over before you start talking. You can say "Here is a list of my concerns."

I suggest that you start keeping good records of all of your tests and appointments and symptoms. Some people are OK with relying on electronic files. Mostly I prefer to keep paper copies and CDs of scans. I bring a tote bag with all my records to doctors appointments.

In my non-medical opinion, your doctors should be considering/eliminating the following diseases (sorry, this may be scarey-- remember, I'm not a doc and I'm typing fast b/c of my eyes)
These are where your syptoms and mine overlapp.
Arthritis group
Spondyloarthropathy (multiple sites of muscle-skeletal pain)
Ankylosing spondylitis - lower back and hip pain
Psoriatic arthritis- skin symptoms and joint pain
Instestinal issues- my rheumatologist says that mine gut issues are connected to my autoimmune disease.

***
Be aware that you may get mental health problems from all of the medical mysteries and gaslighteing. Anxiety and depression are common. I have a great therapist, who is great, I think, because she suffers from chronic health problems, too. Healthy people can be really clueless.

** I need to stop and rest my eyes. I hope I haven't scared you. I hope you feel empoweered to take some forceful steps (If you need to be pushy. maybe you won't need to be pushy with the doctors.)
Step one, get the antinuclear antibody test. Go to a good rheumatologist.

Best wishes. Be strong. Be not afraid! (Boy, I hope that I don't sound like a bossy, know-it-all jerk in this post...Your situation sounds like mine was 10 years ago)