I really sympathise as I had this last summer - it is really unpleasant and can make you feel very anxious.
Has your GP tried the Epley manouvre? It shifts the crystals in you ear which are causing the vertigo - you may need to have it done more than once. It may well make you feel worse for a few days while your brain adjusts but, don`t panic, that will settle down.
Some people get better straight away but I found that although the extreme vertigo improved I was left feeling quite "car sick" and unsteady walking around and I also had problems with my vision - especially using the computer. All in all the problem lasted about 10 weeks but now I am absolutely fine. If it came back again I would try the Epley manouvre immediately. I did try medication - can`t remember the name - but it didn`t help me