Smell only I can smell

Under my Couch I can smell the really gross smell. It's like cat piss cross lemon pepper. Nothing is able to get underneath so nothing has died and the cat has defiantly not pissed. Mum and the next door neighbour can't smell it and they have a really good sense of smell. I don't know how they could miss it because it is so strong. Mum even shampoo the carpet and it is still there. I can smell it from the other end of the house. It has only happened the past few days and it is the first time it has happened. Is there something wrong wit my nose?