Talk to Gynecologist on When To Take Home Pregnancy Test

aoa I missed my periods this month my periods mostly come on cd 27 or 28. during this month I had a spotting for 3 days i.e cd 16,17 and 19 as I don't kniw exactly when I ovulate so can't tell dpo. Well my last period was on 11 Oct so my expected periods were on 7th or 8th Nov but I just had back aches and missed period I got home test and it's negative what are the other possibilities than pregnancy why I missed periods and BTW the days in which I had spotting it was actually a single spot of blood happened once a day for 3 days should I wait and take test again