early pregnancy

okay.. so me and my SO had unprotected sex about 3 weeks ago.. and i started what i thought was my period on the 19th. it wasn't heavy, and it only lasted 3 days. well a few days before that i couldn't eat for about 4 days bc everything i thought of made me sick. 🙄 well.. i took a test yesterday and it was negative. could it just be too early or what?