I used “NOVELON” for last six months to re

Patient: I used “NOVELON” for last six months to regularise my menses. I stopped using medicine in the month of Mar. My last menses date was 03 Mar 15 but i found mild bleeding(just used only one pad) on 18 Mar 15. I missed my menses on 03 Apr 15. Done pregnancy test on 08 Apr 15 found negative. Repeated on 21 Apr 15. “possitive”. I want to know when i had conceived actually?

Doctor: