Hii..I M 28 Years Old...I Have Regular Periods And Last

Hii..I m 28 years old...I have regular periods and last month it came on 18 aug....I dont use condom and had regular sex with my partner...in sept I did pregnancy test on 20th morning but it came negative....now my periods are 6 days late...I m confused tat I m pregnant or not....should I do the pregnancy test again...plzz tell...