Had period 2 weeks after sex last month and negative hpt 3 weeks after. now a day before expected period, slight breast discomfort? can i be pregnant?

Breast Discomfort: Yes you could be depending on your sexual history, it is unlikely this is from the episode 5 weeks ago but not impossible. Some women have bleeding they think is a period early in pregnancy and home pregnancy tests are not 100% reliable although very good. Breast tenderness is not a reliable sign of pregnancy. If you miss this period then you should go get a blood pregnancy test at a doctors.