<s>[INST] Hello, -My last period was June 24th and my cycle is 28 days very regular. -I had intercourse July 11th and 12th.-I had a strange headache July 18th and 19th-My period was suppose to come yesterdayI am wondering if I could do a pregnancy home test today and get reliable answer? [/INST] Hi, I have read your query and feel your concern is valid.The egg release takes place 14 days prior to next expected menses. Your next menses were expected on 22 July. So the egg release was expected around 8th July. The egg has got a life of 24 hours while sperms are active for 3 days. Hence a week around day of egg release is considered as fertile period. Your intercourse does fall in this period. So, there is a possibility of pregnancy.I would not consider headache for pregnancy possibility.The urine pregnancy test and ultrasonography give reliable results 8-10 days after missed period. So please wait for that period and if you do not get menses by that time, get either or both of these tests done. Beta hCG tests are more specific and sensitive, hence they give reliable results even after 2-3 days of missed period.I hope you are guided properly. </s>