Welcome to Connect ENT @abid
You certainly have dealt with this for a long time now. It sounds like symptomatic treatment has been helpful despite no true diagnosis. I didn't have much diagnostics for my vertigo as it was assumed to be associated with my surgery, but then later when it recurred my doctor tried the Epley maneuver for BPPV and that improved it a lot. I still have periodic dizziness and occasional vertigo that I can control with Prochlorperazine, but sinus pressure and headaches seem to bring it on. Have you asked for a referral to a specialist for this problem?