Periods Return after Finishing Tamoxifen

Hi everyone.
I completed 10 years of Tamoxifen in November 2020. My periods had stopped in March 2020 and had been irregular for the past 3 years with breaks between periods of up to 3 months sometimes. They originally had stopped during chemo but returned after I finished treatment and I always had periods whilst on tamoxifen and the oncologist was worried. My oncologist had told me I was in Menopause when they had stopped altogether and was surprised I lasted so long without entering menopause as I was 36 on diagnosis. I finished with my oncologist in November after 11 years. But in December my periods returned and are regular every month since. I am just wondering if my breast cancer was Oestrogen positive and I have no tamoxifen to help with levels is it dangerous to have periods. I had a left side mastectomy but still have my right breast. Would love some advice as I cannot call my oncologist anymore.