Why can't you renew your prescription ? where is your doctor ? If you need synthroid to keep your body functioning, you better continue take it...
From what I konw starting and ending Thyroid medication should be done very gradually, I don't know if a abrubt discontinuation has serious sidefects other than that of hypofunction of the Thyroid. You may want to search the forum for a better answer.
You don't mention anything about your circumstances. Is it not possible for your pharmacy to forward a renwal of your prescrption to your physician? You could also try to get a renwal through an Urgent Care Clinic - it might help if you have a recent report of your bloodwork.
I hop this was helpful.
Sincerely Katherine7