Look up the differential diagnosis for vertigo on WebMD, that should be enough to scare the daylights out of you. Lots of people get this for a few days or weeks due to a head
cold (labyrinthitis,) mild barotrauma or bad luck (benign positional paroxysmal vertigo) but it is not common for it to last four months. Barotrauma should be improving by now, so your doctor is probably going to order an MRI just to make sure there isn't something worse going on, such as a mass lesion- which is extremely rare.
It may take months to get an ENT appointment. Go to your family
doctor with your research
and consider an MRI now unless there is an obvious cause such as chronic serous otitis media or a ruptured tympanic membrane.