This happens to me too and I get myself all worried! I always wait a couple of days to see what happens and if it still seems off I take a test just to put my mind at ease.

If you're worried there is never any harm in doing a pregnancy test. But sometimes with Endo you can have no pattern at all, when I used to have periods it could be constant bleeding for 6 hours or 3 months and I could have 2 days or 3 months in between each period and I could never predict what it was going to be. Clear blue have tests you can do at anytime in your cycle - of you test and it's positive whilst bleeding see a doctor but it doesn't necessarily mean you have miscarried because people with Endo can sometimes bleed slightly during the first few months but it's safest to see your doctor because miscarriage can be life threatening at any stage if it's not fully expressed from the body.