Constant Burning In The Opening Of Vagina

Hi, at the start of last year i got really bad cystitus and after having been treated with anibiotics i was left with a constant burning sensation just on the inside of the entrance to my virgina, ive tried every single treatment for thrush and nothing works, theres no pain or discomfort during sex with my husband, if anything it seems to go for a couple of hours after and then its back again, it seems worse when im sitting down and goes a little when im walking around it does not burn when i go to the loo and there is no discharge...this is really getting me down please help.