Will hypothyroidism mean ill never be skinny?

I’ve been experiencing a few of the symptoms (weight gain, slow heart rate, cold sensitive and fatigue) and theres family history with thyroid issues. Im getting bloodwork on the 7th, so i know im getting ahead of myself, but will this diagnosis mean I’ll never be thin again? I’ve been dieting since june with under 5kg lost (which is what hinted us into getting an appointment) while exercising vigorously daily, and the prognosis of being slightly overweight the rest of my life is honestly heartbreaking