Hi K.,
How much urine output are you seeing when you go? You said you don't hold it until it hurts, but can you hold it or would you leak?
If it's a very small amount of output, maybe you have a recurrent cystitis (bladder infection that never quite goes away) or a sensitive sphincter? I know you can hold it, but does it leak at all when you sneeze or cough? When you go, is the color very clear (like water) or do you see some color from red blood cell break down, yellowish? the yellower/darker it is, the more your kidneys have been working on it and/or you could be dehydrated or sick. The clearer you are could actually indicate issues with your kidneys as well, as they may not be processing your blood very well (they clean the blood and move waste out in your urine through osmosis, so your blood filters through the salty parts a few times until it moves to the bladder for exit.)
Have you seen a urologist for a urodynamic analysis? Kidney, bladder check, blood tests, dye injection to check for 'backwash' into the kidneys...etc.
There are a few surgeries that can help fix a sphincter that does not respond to kegels, and there are medications that can help with the going all the time urge thing, but if I were you, I'd have my doc run urinalysis for white blood cells or other issues/proteins in the urine and blood tests for stuff like diabetes, as both diabetes mellitus and diabetes insipidus will make you have to pee nonstop. Diabetes insipidus is a lesser known type of diabetes that can happen to people and is not related to insulin issues, however it's constant miserable thirst quenching followed by high volume urine output though.
One other thing it could be is stress or if you are taking certain medications.
Figuring out what the issues are with your doc would be the key to fixing it though.
I am wishing you much luck with all of this! I can imagine how awful that must be. But walking in to your physician's office with a clear picture (or even a list---they seriously hate that by the way) of what your pee schedule/ urine output per day is like, and not taking the brush off from your doctor and advocating for yourself from the get go (I need a specialist! I need a blood test and/or a second opinion!) will help you figure this kind of thing out a lot faster than trying to live with it like you have for the last 3 years. 24 is very young to have sphincter/bladder issues, so I am sending you lots of good healing thoughts!!!