Betnovate / How long to work?

Hi all, I've had psoriasis for a long time but in recent years it's spread all over my body and got quite bad. I've also been a bit sporadic with using betnovate but as I'm on holiday at the moment I thought I'd get serious and try to clear it up properly while I'm away. Saying that, I've been applying betnovate routinely (twice a day for a week now) but other than less scales its no less redder and looks pretty much the same. I'm now a bit worried it's not working as previously it would've had a better effect (albeit my psoriasis is worse than it used to be). My question is - how long has it taken you to clear it up by routinely using betnovate (or equivalent brand)? Do I need to accept that it simply isn't working any more? Thanks for any replies!