I have sinonasal cancer - no symptoms except a blocked nose and loss of ability to smell. I was shocked that my symptoms turned out to be cancer and it's been a rollercoaster ride of scans and appointments and operations since. My point is, my type of cancer wouldn't necessarily cause tiredness, but everything we have to deal with, all the emotions and worries and waiting on results is really draining. I have days when I don't want to do anything because I feel so tired. So much emotional stress is bound to have an effect. I don't know if it's the same for you as you said you've had tiredness for a while, but now you've been diagnosed and have to go through this whole, scary process I'm not surprised your tiredness is worse. You don't sound stupid. Just be kind to yourself and rest when you can.