vauxhall vectra is smoking?

hi my vauxhall vectra was doing bunny hops, i changed the spark plugs which has cured the hopping but it dosnt have any power , i never changed the leads just the plugs and is smoking white smoke from the exhaust, it is not loosing water, i have had the car for 2 years and it has allways smoked a little bit the last few days it is getting worse have you got any idea what it is