The former Blackburn Rovers hitman is hoping he is in contention for a place in the team for the Carling Cup semi-final first leg at West Ham on Tuesday night.
Derbyshire said: "It's been very difficult for me. I won't lie to you.
"I haven't been given a massive opportunity at Birmingham City so far.
"I was obviously thinking 'is this the right place for me at the moment?'
"But hopefully this can be the start of things to come for me back in England.
"The manager told me to be patient and that my opportunity will come - which it has done.
"I still believed in what I can do and my head never dropped and I never spat my dummy out.
"I've worked hard on the training ground and waited for my opportunity to come. To score two goals and win at the weekend was massive."
Derbyshire was in the Blackburn team which lost a League Cup semi-final to Manchester United but he is confident of going one step further with Birmingham.
He said: "Manchester United were the favourites last time I played in the semi-finals but this is a 50-50 shot.
"If I looked around both dressing rooms, I know which dressing room I'd rather be in and that's Birmingham City's.
"The lads are buzzing about this tie. It's a chance to pick up a trophy, a very good chance to pick up a trophy.
"Teams may never get this opportunity again so you have to grasp it with both hands and go and play your normal game."