I got elevated tsh after mycoplasma pneunomia. the values fluctuate up and down (4-7) anti-tpo negative. why?

Mild abnormality: A TSH of between 4 and 7 means that your thyroid function may be slightly low. You may not have any symptoms related to this. Despite the negative tpo antibody, the most common cause is still autoimmune thyroid disease. You should continue to have your level checked. If the TSH goes above 12, it likely will be time to start thyroid hormone. With symptoms, one would start treatment earlier.