It is entirely possible that the removal of your thyroid has caused some of your symptoms. Here is a list of possible effects from the surgery which can cause hypothyroidism:
Symptoms of hypothyroidism include fatigue, exhaustion, feeling run down and sluggish, depression, difficulty concentrating, brain fog, unexplained or excessive weight gain, dry skin, coarse and/or itchy skin, dry hair, coarse and/or thinning hair, feeling cold, especially in the extremities, constipation, muscle cramps, joint pain, carpal tunnel syndrome, increased menstrual flow, more frequent periods.
It is also true that an event like this can trigger a latent mental illness. Type III Bipolar Disorder is one example. Hormone shifts of any sort can cause mental issues.
And anyone with a mental illness could also end up with a physical illness, so why not the other way around?
I'm sorry that your parent's are resistant to what is going on with you - is it possible for you to see your doctor by yourself? And have a list made up ahead of time on symptoms you are having?
Start a simple diary/journal with your physical and mental symptoms for a few months and bring it in the the doctor.
If the depression is severe SEE A DR RIGHT AWAY!!!
Everything you said made sense - don't worry about that... We just need to get you feeling a little better!!