What scares you

Pls ooo help me I did pregnancy test and it came out positive and I saw my period on the 17th of this month which suppose to be my 1month old. After my period am still feeling the symptoms of pregnancy ,lastwk Saturday I went back to lab and it still showing positive so I decided to go for scan yesterday and my result says am not pregnant .... I did another lab today the result is positive .am just confused on which to believe lab or scan . my question is it possible for scan not to detect the pregnancy?