answer please

Hi my period was 7 days late (never late) i had bright red bleeding for 2 days with sharp cramping above my V,  not the regular AF cramps was not that heavy but noticeable, didn't soak a pad then light brown CM with like ewcm, all for 4 days total, since then my stomach has been feeling fuller,  and cramps as well as my back, took a test and had my blood done at 5 days missed AF and it was negative, what is the cause of this lateness? And is bright red blood a concern? Anyone had similar?