Awful! Some find that Vagirux which is cheaper than Vagifem isn't enough - it may be a reaction to the fillers or packaging, rather than the active ingredient. I would stop for 2 nights and apply KY Jelly to ease any itching and contact my Surgery for Vagifem; a pessary; or 'estriol/ovestin', a cream inserted by applicator.
Is there soreness, itching, redness 'down there'? Sometimes the vulval area can react. The idea with VA treatment is to use every night for 2-3 weeks and then decide whether symptoms are kept away with use i.e. every 3rd and 5/6th. nights. Some require nightly treatment.