Black stool and vomit

Hi sorry such a disgusting topic, but a little concerning for me. I am on tamoxifen Genox20 brand, Christmas night I had a vomit (only time since) and it was black as, and my stools have been black as well ever since, even today??  I am coeliac as well so not sure what is going on !!!!! I am extremely tired and no energy.

Wondering if anybody out there has had this happen and why, not sure if its the tablets or just too much rich food for Christmas day.

Any help would be great. Cheryl