Period 8 days late positive not pregnant always give or take 3 days for my cycle keeps gettinglonger

I suppose my first question would be, how old are you? The length of your period can change as you get older, or if you are still young you may not have found your natural menstrual cycle lengths.

To give you an idea of what I mean: When I started my periods when I was 13 it was every 28 days for exactly 3 days cycle length. Now that I'm 35 I notice that they now vary between 23 and 29 days so I'm never sure when I'm due!

The other thing that springs to mind is (as you mention you aren't pregnant) are you trying to get pregnant? Stressing about whether you are or aren't pregnant can cause your menstrual cycle to be later than usual. I have been trying to conceive myself (for 2 years) so I often notice other 'symptoms' that I may or may not have that makes me think I'm pregnant when I'm not thereby causing my period to be delayed.