Could I be pregnant or something else

Hello I'm new to glow well my question is:  I had unprotected sex on March first I am on birth control but prior to march 1st I had missed three doses well anyway I had u protective sex on the 1st and on the 8th I started having brown spotting which I know is old blood because I have had that before but ony like three days before but this Time it was brown spotting for one day and then for the next it was light pink spotting. For the past two days I have felt nasuea at certain times like once in the afternoon