Thyroid Cancer, now chest pain

Hi,
I am a 25 year old female who was diagnosed with Follicular thyroid carcinoma & Hurthle Cell adenoma in June last year.  I had radioactive iodine ablation in July.   I have not been well since, I had an enlarged lymph node with reactive changes in the posterior triangle and have suffered severe hypothyroidism at times due to overdosage of Thyroxine.

I am not overweight but I do smoke.  I now am suffering chest pain just below my left breast behind my ribs, heart pain I assumed.  I currently have not been taking any Thyroxine so I can become hypothyroid for my followup Whole Body Scan.  My doctor ordered an ECG as she believed it couldn't be related to hyperthyroidism (which causes tachycardia) because I haven't been on any thyroxine.  I've had a resting heart rate of 103 bpm at times and when I saw my doctor she said my heart rate was through the roof but blood pressure was normal.
I've also broken out in a cystic rash/acne on my chest which has never happened in my life.  My ECG said I had a right bundle branch block.  I am also suffering from tachycardia quite often.

I'm still suffering the chest pain, and I am worried about pulmonary embolism or metastatic thyroid cancer, can these things cause right bundle branch block? I'm assuming if it was a pulmonary embolism I'd be dead by now.
My fathers side has all died of heart disease, my dad now has the beginnings of it, and my maternal grandfather died of a heart attack instantly at the age of 65.  I realize I am young, but I am very worried due to already experiencing cancer.

Thank you for any advice, information or help you can give me.

[cocomadam]

Severe hyperthyroidism i mean