Hello. Welcome to hcm
I want you to understand what is happening with you. Normally when women menstruate,they shed blood and their thickness of endometrium remains thin,so only mild pain. But for you,due to many causes,there is lot of blood(products of menstruation
) and your uterus
tries hard to expel. while doing so,it enlarges. It can be normal too but should be evaluated properly. If the thickness remains same in next cycle,you should be evaluated with biopsy
so as to rule out malignancy(not common in your age group) but still we need to be vigilant. Hope your doubts got cleared.
All the best