Can you still have this condition if you have normal electrolyte levels? Do I need a definitive test to rule it out?

I have interstitial cystitis and chronic pelvic pain syndrome and pee average of 13-20 times a day though it can be much more if I consume a trigger food/drug/medication. I've seen some people in the IC sub say they have diabetes insipidous as well.

I always feel dehydrated, even if I drink over 5L of water in a day. Drinking low amounts of water doesn't impact my urinary frequency until I go like 8 hours into the morning without drinking or eating and eventually run out of urine. Then even having a sip of water is enough to make me soon need to pee. My urine is usually clear, it's only more yellow if I go for several hours without drinking.

My mouth is chronically dry. I hardly produce saliva and I experience sporadic pain in my salivary glands/cheeks about 10-60 minutes AFTER I eat food, which doesn't appear to correlate with any particular foods, it can be anything. The pain can happen several times a week or not happen for months, on and off for like 20 years.

Other symptoms that may be unrelated or not are I always feel tired and weak, difficulty falling asleep, I have muscle pain in my arms, legs, sore shoulders and neck, chronic lower back pain, pain in wrists on the palm side, my index fingers have started to feel pain in the same joint on each finger when gripping drumsticks which has never before been a thing in my 18 years of playing. These symptoms have me thinking of arthritis (which my nan had), fibromyalgia, chronic fatigue syndrome. But I'm not diagnosed with any of these and I haven't tested positive for any antibodies, though I know most patients with those conditions don't have antibodies anyway.

I have been tested for diabetes mellitus and tests suggest I don't have it. The specialist I saw believes I wouldn't have diabetes insipidous because I have normal electrolyte levels, but I don't know if that's true. I wouldn't be surprised if diabetes insipidous is not guaranteed to cause electrolyte imbalance.

I think the definitive test is a blood test for vasopressin right?