No sex missed period

I never miss a period -that’s not normal for me anyway and not having sexual intercourse at all , I’m not sexually active , what could be the cause of a missed period ? I’m not stressed, have medicine that I’ve been on for a year and never missed a period since having a baby 7 months ago. I’ve tested 2x already which obviously was a waste because as I mentioned firstly . Just to set my mind at ease ya know? The second test I took had a faint horizontal line when it should have been a vertical line . I’m trying not to stress too much but hey help a sister out . Let me know what u think