My 5 days menses perid is completed the next third day we did sex so can I get pregnant

Some say it's around the 12-14 day mark after your* menstruel period, when your ovulating. So if you are trying to get pregnant, try around that time.
However saying that, it is possible but unlikely.

You can always get pregnant.
The probability might be lower nearer your menses, but if you are in the 10% range and you are one of the 10%, then you are 100% pregnant.

Plus, they are just averages over the entire world. Each woman is different from each other woman, and each woman is different from month to month.