Hello Hayley, I am really sorry to hear this about your health but suggest you not to worry.
We say in medical fraternity, that if God asks us to pick up one cancer, we will always choose Thyroid Cancer!!
It's that good curable..

Hi and welcome to HCM..
I thank you for posting your query here and I'm definitely going to help you out.

I being a surgeon, we encounter so many such cases day in and day out..
I read your question completely and have understood it well enough..

I will analyze all your points and provide necessary explanation..

1. Last year March thyroid cancer, so it's roughly one year now since you finished proper treatment.
Surgery and Radioactive Ablation..
I am really happy that you have received standard treatment..

2. Last dose or treatment, November.
Meaning 6 months passed by..

3. Since, you already have a 2 year baby, I suggest you following things..

A. Suggest you to wait for maximum of two years.
Post last dose of Radioactive treatment.

B. It's not compulsory. But I don't want to see any developmental anomalies in your 2nd baby, hence advising this to you.

C. Various articles say, one year is enough. But always beneficial if you can wait for 2 years post last dose.

D. Also, in future after you conceive, please don't forget to check out developmental anomalies if any..
Radiation of any kind is notorious for such problems..

Hope this helps you, in case you need any further assistance, please let me know.
Take care and God bless..