Will corticosteroids intensify the symptoms for hypothyroidism like fatigue / headaches? i have all symptoms for low thyroid but bloodtest says negtiv

No: Corticosteroids Don't affect underactive thyroid status unless there is inflammation of the gland. There are several tests for thyroid status and if you're still concerned about your thyroid status, have a thyroidologist evaluate and advise you. Some conditions like anemia, low blood pressure, chronic infection, low iron levels, depression can mimic an underactive thyroid. These tests can be done also.