Advice or guidance please

Hello, so i am 19 years old and have been with my wonderful boyfriend for 4 years now. I am not on birth control but we do use condoms every time we are sexually active. My period arrives every month on the 20th. Not a day early, not a day late. Its is now the 26th, about to be 27th in a few short hours and it is still not here. And i am having no signs of it arriving. Now i do know that condoms are only like 98% effective so i did take a pregnancy test yesterday and it came back negative. Anyone have any ideas as to what could be going on? I have not had any changes in my diet or any added stress eaither. Should i wait a few more days and take another test? Should i possibly schedule a doctors appointment? Any in sight would be greatly appreciated. Thank you.