what could be problem-oil?

I have a renault clio,automatic. Recently i've noticed when i start car and go to drive off,acceleration is really hard,i have to really push down to make it go whereas before i didn't,so obviously something's changed,could there be an oil shortage in gearbox? At traffic lights etc its not so bad,i only use car at weekends at the moment so wasnt sure if thats the reason.any ideas?