Period on Tamoxifen

I saw my oncologist last week and he said if my periods came back I would need to contact him about having an injection. I started a period Monday this week (they had carried on until my 4th chemotherapy then stopped - I had 6 FEC ending in late January, then started Tamoxifen early Feb.) I rang his secretary on Wednesday but haven’t heard anything. Is this injection Zoladex? How soon should I have it?