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Your period is delayed by 3 days,but according to you period was light and lased for 3 days in all probability it should be your period.
If you have doubt just take urine pregnancy
test if it is negative indicate that no pregnancy.
Even better is blood Beta hcg
test which more sensitive than urine test which will clear your doubt.
You can consult Gynecologist and she will examine you internally and if required a transvaginal ultrasonography
can be done if there is any doubt.
This will certainly rule out pregnancy and clear your doubt.
Hope this information helps you.
Dr.Akhilesh Dubey M.D