Hypothyroidism can happen at any age but most often occurs after child birth or in middle age. that doesn’t mean that you don’t have it or the test results aren’t right. It’s just that “ranges” are based on a group of individuals “normal” not “your” normal.
If it’s been some time since it’s been checked, have it checked again and see if there have been any changes.
If your not happy with your Dr’s diagnosis or treatment research other Dr’s. If you’ve used an endocrinologist next time look for a OB/GYN they might be more responsive to your complaints.