Hello and welcome to EmpowHer,
First of all, I want to say how sorry I am that the doctor did not do his job and tell you that all your symptoms are being caused by your enlarged thyroid gland and Tinea Nigra. You are not pregnant. However, your enlarged thyroid and symptoms indicate that you may have Hypothyroidism and you need to get treatment before it gets worse!
Be aware that because you are so young, most doctors will not believe you have hypothyroidism and will simply give you birth control pills as a treatment. However, based on your symptom history, you may need to take the treatment for hypothyroidism called Levothyroxine.
Don't be afraid to push for more testing and better treatment until your symptoms resolve!
I encourage you to read the article below that lists common symptoms that indicate your thyroid is not functioning properly.
I wish you all the best,