You may have just taken a huge shortcut in treating your depression - and have your mom to thank for it. If it turns out you are hypo, you may not have depression at all and wont waste years treating that while other symptoms go undiagnosed and untreated.
Do have the tests done - hope your doc is willing to test for FT3 as well as FT4 - though most tend not to - and go on from there.
I have been treated for depression for 10 years and I'm not convinced after all of that time that it wasn't Hypothyroidism that entire time - don't waste your time - do the test - it's only time.
The treatment for hypo is fairly well tolerated and straight forward. You will not die from it or anything but you will need to treat it. Depression is a harder diagnosis to swallow - much more difficult to treat and most meds are not well tolerated.
Take care.
Many many people get treated for depression with no doctor ever thinking to check the thyroid levels. I have personal experience in this!
What are your fears in knowing you have a thyroid disease? Treatment is simple of very effective for lots of people. The people on here unfortunately aren't getting the respect or dosage they deserve and so of course, you will hear their stories of gloom and doom, but it is not all bad! With correct treatment you will more than likely find the depression will lift.
Does your family have a history of thyroid disease? It sounds like your mum is right on the ball!
Cheers!