If the prism RX is correct -it should help immediately. It could be that you just have a very difficult/ possibly impossible problem to correct OR you may need a different prism correction. You should be rechecked by the doctor who prescribed prism glasses to you. Don't worry - I am never surprised by patients like yourself having trouble with prisms. THey can be very difficult to get exactly right and sometimes we just have to give it our best possible educated guess after many, many measurements. IF first doctor can't get it right after 2nd try - definitely see a pediatric ophthalmology specialist as recommended above.
MJK MD
When I developed double vision, it was my experience that many eye care professionals (both ophthalmologists and optometrists) are not terribly skilled at prescribing prism. My first couple of prescriptions made little/no difference in terms of my vision. It was not until I saw a strabismus specialist that I got a prescription which actually worked--within a couple of hours of wear, most of my double vision was eliminated. If your glasses with prism haven't worked after almost a week, I don't think they ever will. My best suggestion is to see a different doctor--someone who specializes in treating strabismus, either a pediatric ophthalmologist or an optometrist who treats strabismus (sometimes called a "developmental optometrist.") Best of luck--don't give up!