You may have postpartum thyroiditis (PPT). PPT is considered a "temporary"/self-resolving thyroiditis. It usually starts with a hyper phase, followed by a return to normal and then a hypo phase. However, many women only experience the hypo or the hyper, not both.
TSI (thyroid stimulating immunoglobulin) is the antibody marker for Graves'. If you have that tested, and it's elevated, you'll know you have Graves'.
Did they test FT3 or TGab (thyroglobulin antibodies)?