Thank you for writing!
If you haven't had sex since your last period, then you cannot be pregnant. A pregnancy test from the pharmacy can confirm this if you would like peace of mind. Some people like to see the result of a test "in black and white" to be reassured.
Other reasons for being late include hormonal shifts, a change in body chemistry or a physical or emotional change. During these recent times of isolation and the additional stress it can cause, your cycle may have changed.