What could be the possible medical issues that can prevent weight loss?

Hypothyroidism: One quick one would be under active thyroid. Thyroid hormones help regulate metabolism, so if at a low level - weight gain can occur. Go to your pcp and get the levels (tsh and t4) checked.

Multiple: Doctor already mentioned thyroid deficiency, cushing syndrome, depression, sleep disorders, hormonal imbalance and medication side effects are some of the medical issues.

Weight loss: There are many conditions that may make it difficult to lose weight. There are various hormonal imbalances you can have like cushing's syndrome or hypothyroidism. You should consult with your primary care physician.

Hypothyroid: Main medical cause interfering with weight loss would be hypothyroidism or another medication interfering. Talk with your doctor.