 [ Symptoms ] how does severe headache relate to heart disease [ Disease ] hello and welcome to ehealth forum if you are having normal periods 4 5 days that you usually have then you can never become pregnant by having unprotected sex during your periods however if you have a 26 28 day cycle or a shorter cycle of 24 26 days and have periods for 7 8 days then you need to be careful on the last 2 days hope this helps take care