You need to have it re-checked by the people that fixed it - they need to make good on the repair before you end up with a trashed engine and expensive repair bill! I would do it tomorrow. Until then I would check the oil daily.
Do you see oil leaking under the car? It may be an oil pressure switch or something easy. It could also be an upper intake. Also the rear crank seal plate gasket are known to go bad on these engines, (this requires removal of transmission to repair that).
Get it checked!!!!