Period after several years

Hi, I was treated for BC in 2021/13 - involving surgery, chemo and radiation followed by tamoxifen and then letrozole. I came off letrozole in January. my periods never really resumed after chemo and so I would say it's at least 5 years since I've had any period, including spotting, etc. My blood-work from 2/3 years ago indicated I was in menopause. This week I have a full on period with a good bit of discomfort in the area of my stomach where my uterus is and involving my left ovary. I'm wondering if this is common and could it be my body adjusting to coming off the hormone treatment.
I've had some pain in my non-effected breast which I went to the GP with and have an appointment in the Breast clinic early next month. I'm wondering will I just wait until then or should I have the occurrence of the period checked before then? If it's common I'm happy enough to wait. Thanks for your time. I'm 50 years old.