Feel extremely depressed as i suspect i have an intellectual disability - should i see a doctor to confirm this/seek treatment?

Depresion: Absolutely don't diagnose yourself as it only causes more confusion and further depression

Educational pysch: for intellectual testing you should see an educational psychologist. They are able to do testing on your IQ and learning. For the depression you should seek care from a doctor. You should also find a counselor to talk to, so that you can work through issues you are having. Medication + counseling works best. If you are considering suicide you should go to the nearest crisis center NOW.