Just guessing, but it sounds as if, yes, your thong was too tight. In addition, it sounds as if you may be having an allergic phenomenon to the material and/or the color of the thongs.
Methinks avoid all soaps; clean primarily with tepid water and/or Cottonelles. You will need to exercise more care in the future, or it will recur.
For quick healing and comfort at this time, buy some Eucerin cream or ointment and glob it on the affected area 3 times daily.