1st and foremost...STOP DRIVING YOUR CAR! as you have a major failure from either piston rings, headgasket or valve guides - it needs some major overhaul and the more you drive it the worse the damage gets...you might be lucky and not have a warped headgasket after that long trip

to help diagnose your problem when the car is running and cold pop open the radiator cap (don't worry so long as your car has been sitting for at least a couple hours) then look for bubbles in coolant...if there are bubbles headgasket for sure - which would explain the white smoke (burnt antifreeze), the bogging down and the o2 sensor code as it get mucked up

you can also get a compression and leakdown tests done to determine the extent of the problem for each cylinder and this can find if you have piston ring failure...however it is most likely you'll need a total engine rebuild...i'd look into a good running used engine and just replace it unless you want to try your hand at doing your own rebuild