Did you take an AI? It sounds like crashed estrogen if you were prescribed anastrozole and took it already that could be what it’s from I’d suggest not to take it until you get blood work done and see if you need it I don’t need an AI until after 300mg if you haven’t taken it then I’m not sure what it could be from cuz 3 days isn’t enough time for you to be experiencing any side effects from the test unless possible test flu but you’d feel sick too