Period last month was 2 days. this month i tested positive. i would be 3 weeks, is that possible or was last month implantation?

Estimation gestation: in view of your question, it will be nice to know the first date of your last menses. For the sake of clarity based on 3 weeks gestation today: Probable date of conception: 8/8/17 last menses: 7/25/17 estimated due date : 5/1/2018 As you can see, it is most likely you conceived on 8/8/17 based on the information you provided.