Check the Coolant level m8... If it down then it sounds like one of the following probs'
white smoke is coolant getting into the combustion chamber .. (exit's exhaust as Steam)
a) you may have a cylinderhead gasket gone.
b) or hopefully Not, a cracked cylinder liner.
Did this only just happen after you oil change or has it been smoking for some time?
see if you can get a coolant pressure test guage and do a pressure check in the coolant system,