What are the symptoms of an overdose on kelp tablets?

Yesterday and today I have taken two 150 mcg kelp tablets...(they're basically just iodine, right?). Anyway, tonight I am so nauseous, vomiting, very nasty abdominal pains...could it be the kelp tablets? I am taking them because I have pretty much every hypothyroid symptom there is and wanted to go with a natural approach.