Flashing oil light?

I been driving my 2003 corsa when im driving the oil light keeps flashing sometimes when the car is still and sometimes when its moving but other times drive it comes off ?? im really worried im not sure what this could mean as there is no oil leaking out from the bottom i went to a garage and they cleaned out the car and said take it easy so i did and now its doing it again he also said that it was not the engine or the the gearbox can anyone help me please!! thank you