2001 Volkswagen Jetta Engine Oil or Motor Oil

i got my oil change 2 months ago, i still had 900 milege left, i cange my oil every 3000 miles, so i checked my oil today and there was no oil, like nothing. i went to the work shop there were no leaks. So i got my oil change. I have no clue why there was no oil. I installed intake and a muffler thats all. Can you please tell me what should i do.
thanks