Do I have damp?

I don't really know which tradesman I need, however..... There is a foisty/musty smell in my house, the worst room is the front bedroom (seems strongest towards the window/front). I have cleaned thoroughly and it has been decorated (I have no carpet yet). Is it possibly a problem under the floorboards? There are no obvious signs of damp anywhere. The floorboards are not wet. It has got worse since the weather has started warming up just recently. It’s awful and I’m worried it might be something serious (like rotting joists).