Hello Tquill and thanks for posting, 

Periods can restart after chemotherapy and tamoxifen, but the older you are the less likely this is to happen. Generally the advice is to let your doctor know about bleeding that is out of the ordinary, so I think it would be sensible to tell your GP - they can make an assessment and check you out. 

I hope you can get a GP appointment easily to get this sorted out,

Best wishes,

Julia