question where do I go to be classified as disabled?

You do not get classified as disabled. There is no disability id card. What you want is your employer to recognize you as disabled for the purpose of a disability accommodation. For this you need a letter from your doctor who states that you need to sit for x minutes every x hours on account of your disability. Your employer does not need to know what the disability is, only that your doctor has written a statement that you have a disability and require a specific accommodation.

There is no "class" for disabled, if you bring a recommendation from your doctor, and your employer doesn't accept it, you'll have to be diagnosed with a physical problem requiring accommodation. Then, if your employer still refuses to accommodate you, you can call the ADA.

if your job cannot accommodate your disability and they cannot make changes without a reasonable cost than the ada cannot do anything about it- the ada can only say reasonable changes- or change positions - what size isw ur company ? smaller companies are not required to follow ada rules

Go to your physician. Because your physician is able to "legally medically certify" you as "Disabled". You can give a written note by your physician to your employer that states on how you are Disabled and what job accommodations you require on the job.

One of the other answers is wrong. You can get "classified" as Disabled. For Example: In the state of where I live in I am "classified" as a "Handicapped Driver" by the Department Of Motor Vehicles (DVM).