What can it be?? It smells sort of...stale. Like old bins or something.
It appeared suddenly...there's no food or drink spills...I only have one small sofa in here and no carpets or rugs. I've sniffed all over the sofa and curtains but it's not them...I can really smell it!
There's a bookshelf, my desk, a combustion fire and one sofa in here. It's doing my head in!