What Causes Irregular Menstrual Periods While On Thyronorm?

I went to doctor for pre consulting about family planning in February and I had some check ups. In that everything was normal except thyroid. It was 5.6. Then I started taking thyronorm 25 mcg. Now it is 2.8. But I think this medication has effect my periods. Now my periods are lil delayed and very less bleeding compared to before. I am trying for baby from last 5 months but no success. I am worried. Is this all because of thyronorm or something else. Previously my periods was regular. Please advice what should I do?