What Causes Bright Red Clots, Pain While Walking During Periods?

Hi im 30years old and had a baby 4 months ago, i have had periods since but they have been normal. I was 2 weeks late for this one and the blood is bright red with clots ,heavy but my concern is that the pain when i walk or need to go toilet is so bad even when i wee i feel like im in labour all over again i can barely move it hurts so much.