Ah Ah, its most definatly the freewheel, make sure the chain isnt too tight, then get hold of one of the teeth on the freewheel, and wobble it side to side, it shouldnt move, well only a very tiny bit, but yours, since its clicking, it might move quite abit, to sort it, take the crank arm off, then on the freewheel, turn the crank so its facing upwards and there should be a ring on it with 2 little notches in it, get a screw driver and turn it anti-clockwise, it should tighten. but this means once you start riding again, its gonna come loose, so if your dad can weld, ask him to put 4 little bits on weld on the freewheel (you probably shoud know where they should go) and then your freewheel will NEVER come loose again (Y)