Hi. Thanks for your query. Noted the history of thyroid disease, ate pizza followed by blood in stool, sandy stools, increased frequency of passing stool, headache and fever. Yes, you should immediately go to ER as this looks to be severe form of gastroenteritis and needs urgent clinical evaluation, examination, proper antibiotic coverage and if need be an admission for a few days for intravenous fluids and electrolytes, antibiotics. Better not to take chances. You need to be investigated and send samples of stool, blood and urine. Blood culture and stool culture helps a lot in future if something serious goes on.