Can a person have symptoms of hyperthyroidism, and then it changes in a few days?

Yes.: Symptoms of hypo or hyperthyroidism can be similar, surprisingly enough. Typically with hyperthyroid, pulse increases, bowel activity increases, weight loss, increased perspiration, racing thoughts...In young people this is often an autoimmune thyroid disorder. Have your doc work it up: the answer is in the blood tests. Symptoms can be extremely variable, and changing.