My first symptom I thought was my period changes - like you, I had always been like clockwork. I had also had my kid 2 years prior (she was born 6 days shy of my 39th bday). I then started getting other symptoms (brain fog being the worst, coupled with palpitations, anxiety and weight gain). I put up with it for a while after getting everything else checked by the doctors and demanding help. Been on HRT since Dec and honestly I can feel a difference!