My son is 9 months old and i gave him 5 or 6 times the recommended does of zyrtec (cetirizine) (3 ml), 2 days ago, he seems to be ok though, no strange behavior should i still worry?

Recommended dose for: a 9 month old: ZERO. To not give medications to an infant without a specific order from a physician. You were lucky. Infant could have stopped breathing

About yourself: Zyrtec (cetirizine) is called a non-sedating antihistamine because most of it does not go into the brain. Only about 7% of people get tired on Zyrtec (cetirizine) versus 93% who do not. From what you state he seems to be in the 93% group. You don't have to worry about the drug overdose. You do have to worry for both of you that he's growing up under a repressive military dictatorship.