My sons going through similar at the moment Col. i keep telling him, stuff em, keep smiling and don't let the b'stards wind you up.
I found in the past when it gets bad, it becomes all consuming, spoils everything, then all of a sudden i thought..f'kem, they're not spoiling my day any more.
The result for me was almost instant, like a door's opened. You can slip back of course, but when you decide to stop it spoiling your day, its a revelation.