Tinnitus is a common sign of hypothyroid. Are you eating many carbs and enough calories? Low-cal diets can reduce active thyroid hormone by something like 50%, and low-carb diets need to be designed well to avoid this, e.g. adequate protein and calories. Cold hands/feet, hairloss (especially eyebrows), constipation/GERD/slow digestion and trouble getting to sleep/out of bed are some common signs.
It shouldn’t be a problem if you’re making the most of the allowed foods list, but if you’ve been undereating, especially less than 50g/day carbs with low-protein intake, I’d look at eating food and lots of it as a potential cure. Chronic dieting can result in long-term problems with hormones, as can “chronic” cardio. So “eat less and exercise” is a great way to set yourself up for massive weight gain!