daf clutch?

Hi All
I have a daf45 150 truck 1999 Reg
The clutch pedal will go hard to push down, I can drive for five minutes or I can go longer before it start to happen. At one stage I pulled up at some lights and could not get it in gear for ten minutes then it when fine and drove off. Is it me not driving it right or could there be something wrong with it . It had is MOT month ago