First things first, take it back to the dealership you serviced it at and inform them of the problem *as a result of their work*, don't let them corner you into any diagnostic fees.

What kind and weight of oil did you have put in and what does it say on the work order?

As for the possible causes, they might have put the wrong weight oil in (ex. 0W-40 insted of 15W50). Low oil level is another, hopefully not, cause.

Are there any oil drops on the ground? How much oil does the engine consume in a given time/distance?