Uncertain

Samantha
So, I'll be very to the point - my period is 12 days late, which is incredibly unusual for me. A day or two variance I typically expect, but 12 days - no way.
My period being so delayed has only happened one other time, I believe it was just this past May/June (if I'm remembering correctly). I eventually got it, however I did a pregnancy test even though I was experiencing no symptoms, and it came out negative. This time, I have no symptoms again but I'm wondering if I should still do a test. I know it's easy to just do the test and put myself at ease, but I guess I just don't know how accurate these at-home tests truly are.
And what I'm also wondering is why my period is so late - is stress actually a factor? As well as being highly emotional? I have depression, plus a heart condition, and I haven't been regularly taking my medication for either (whoops, that's a story for another time though), so could that be a factor? I know there's not necessarily proof or fact, but I'm just curious if anyone else has experienced this, and if so, why? Like how can I keep my period the way I like it - regular and predictable!