Why would my periods stop at 27?

hello, i am 27 years old and reasonably healthy. i wondered if anyone would know of a reason why my periods would stop. i am not pregnant, i have tested at home and at the doctors. i have had a lot of hormone blood tests and there is no sign of early menopause or thyroid issues all the function tests came back ok. i had raised platelets and i have to repeat the blood test next week. i dont know what this means and if anyone can help me out there, please do. my menstral cycle has always been heavy and very painful, i have been diagnosed when i was 17 with menorrhea, which explains the pain but it has never caused me to stop before. i have a daughter who is 6 and thing have been normal after her birth until 5 months ago. the only other health issues that i have is alopecia areta ( bald patches) on the scalp. i was told it could be stress with the alopecia and the periods but although i have lost my job, i am happy and debt free and under no pressure to find employment as i can afford everything i need to pay. i feel positivly carefree infact so personally i dont think stress is an issue. can anyone help? thanks for reading.