Very occasionally I will get pronounced PMS where I get the symptoms you describe (swollen, tender, bloated, and hugely increased appetite). So it could be a bad case of normal PMS hormones. But, I am wondering if the antibiotics have maybe interfered with your absorption of the synthyroid. Antibiotics can interfere with the effectiveness of other medications, so perhaps you should speak to your doctor about the timing of dosages to ensure that you are getting the benefit of everything you are taking.