Hi thanks for your question.
Preggnancy test comes positives 7 to 10 days after the missed period.I think you gone too early for pregnancy
There could be few reasons for your light bleeding.
First could be you have concieved and this is your implantation
bleeding .Implantation bleeding occurs one week after ovulation due to implantation of fertalized ovum in uterus
.The second possibility is you had concieved and you aborted.
The third possibility is abnormal period,which do happens sometime.
The best way to sort out the confusion is to repeat the pregnancy test 10 days after your light periods.If result comes negative,it can be further confirmed by the help of ultrasound
Hope this answered your question.