Well, let me first assure you that most probably your daughter s condition is due to hormonal disturbance (not a serious organic pathology). In the Perimenarchal period, Some girls experience such irregularities especially in the 1st year after menarche. But, since your daughter is taking levothyroxine (Synthetic thyroid hormone), it s very likely that it has an essential role in her menstrual irregularities. L-Thyroxine could put her in a state of subclinical hyperthyroidism that could alter the secretion of female hormones produced by hypothalamus/pituitary gland. I strongly recommend that you seek a gynecologist s medical help who is going to run some lab tests (hormonal assays, complete blood count, and coagulation profile) and refer your daughter to a radiologist who would image her uterus and ovaries to rule out the possibility of having a serious organic pathology. Yours Sincerely, Basim Abuelnor, MD