Regarding upt. To induce my period?

Is 55 days past last intercourse upt reliable and 21 days past intercourse beta hcg blood test reliable. I am not having period without taking norestherone past 4-5 months I have to take norestherone to get my period if I got my period last period on 24 may to 29 may with 2 days heavy flow and 4 days lighter flow and brownish in nature after taking norestherone and this month again I missed my cycle but their is no contact with my partner from 2 may and the contact before 2 may was oral. But I am not getting my period without taking period inducing medicine why it is happening I had test beta hcg blood test on 22 may which was negative and on 25 and 27 june upt which was negative any chance on pregnancy I had started primoult n again from today to induce my period