What next after total thyroidectomy for differentiated papillary thyroid cancer?

No short answer. Ptc treatment depends on age, gender, uni or multifocal, affected nodes, and other factors. If only one site, no nodes, <2cm, between 18-45 yrs old, female then surgery alone with ultrasound and blood testing followup sufficient. Multifocal, male, >2cm, <18, >45, extension outside thyroid, positive nodes, tall cell variant then postop radioactive iodine. Consult with endocrine who manages ptc.
Talk w/endocrinologi. There are several possibilities, from nothing to further surgery to radioactive iodine to long-term thyroid suppression with follow-up. It depends a lot on your finding, lab tests, surgery results, pathology and many other factors. Consult your endocrinologist for more into. This is not something that should be treated by a primary care physician.