I took the pregnancy test this week and it came back negative. i've had lots of stress and i even was sick and lost weight. could that delay my period?

Maybe yes: Pregnancy is the most common cause of a missed period. If not pregnant, other causes of a late or missed period include: excessive weight loss or weight gain, increased exercising, emotional stress, having an illness, traveling, medicines (especially birth control pills), hormonal disorders, etc… A pregnancy test is accurate 3 weeks after sex (3 weeks after when conception might have happened).