Welcome to HCM.
You get period 4 days late and stay longer than usual.Also presents with headache and lower abdominal pain
It is probably due to hormonal imbalance or early abortion
bleeding (as you got light pink color).
You may do a USG scan to evaluate underlying pathology or check remnants of aborted product if occur.Then consult with your doctor.
Avoid stress by doing yoga or pranayama,control body wt,take healthy diet, take Vit-E and Folic acid
supplements to improve fertility