Brief answers:
1) Hypothyroidism is where the thyroid gland produces too little thyroid hormone. Hyperthyroidism is where the thyroid gland produces too much thyroid hormone.
2) If you are diagnosed with thyroid disease, one of the main foods to consider eliminating or limiting are cruciferous vegetables such as broccoli and cauliflower. Link to article that covers this more in depth:
https://www.everydayhealth.com/hs/th...oods-to-avoid/
3) Difficulty losing weight could be thyroid-related. Ask your medical provider to check a TSH and a FT4 for a good picture of how your thyroid is functioning. This is a simple non-fasting blood test.
Best wishes.