sounds like either the crank seal is leaking, or the gearbox seal is leaking.
oil will cause your clutch to slip.
You will need to take the gearbox off to look. Your clutch will need replacing most likely anyway (covered in oil)
But the seal will either be a gearbox rebuild, or a bottom end rebuild.
UNLESS - your clutch slave cylinder is leaking? check the brake/clutch fluid level (do this before you drive anywhere)