Could i still be preganant or is there sumthin else going on?

me and my boyfriend slept 2getha the 5th of this month. and i was supposed 2 get my period on the 20th but now its the 27th. but i took a pregnancy test on the 17th and it was negative. whats going on. am i or am i not? has this happened 2 any1 else. im 2 young 4 menopause and i have a fast metabolism so i dont work out 2 much 2 cause a skipped period. 2 worry or not 2 worry?