so my period started the 14th of july. lasted 3 days. stopped 3 days and started again on the 20th…

so my period started the 14th of july. lasted 3 days. stopped 3 days and started again on the 20th of july. do I go by the first day I bled or the 20th? I took 2 blue dye tests they were positive and 2 pink dye they were negative. no signs of period coming and am feeling slightly nauseous in the mornings and have had lower back pain for 2 weeks