I was prescribed betahistine 3 weeks ago for dizziness and balance still feel unbalanced how long do they take to work or should i go back to gp?

Dizziness: If the dizziness is vertigo affected by head movements it points to an inner ear disorder. Since your symptoms have persisted so long I recommend a consultation with an Otolaryngologist who will treat this type of disorder by manipulations of your head in an effort to get the dislodged small concretion, if there is one, back into place which can relieve the positional vertigo problem.