I agree that we need to see your latest thyroid labs, with reference ranges, since these vary from lab to lab and must come from your own report.
I'd also wonder if you've had potassium and magnesium levels tested. I get cramps like this when I don't take those. The diarrhea, tiredness and weakness could be caused from being over medicated, but I've never heard of Synthrex - can you tell us something about it?
Can you post your most recent labs results with ref ranges?