Start it up ,let it run 1 minute, get in and put it in drive with the brake on, if the engine is shaking you have a non functionaling cylinder that is not firing (igniting and burning the gas) and the unburnt gas passes by the piston getting into the oil oan contaminating the oil,
this could be a quick easy repair or internal damage, You'll have to have it looked at by a local service place chosen by reputation.
g-luck
Jon