Then things are very likely okay. Hcg has stimulating effects on the thyroid. You probably have high levels of it, judging by your severe ms. Since your hcg is stimming the thyroid to normal levels, your pituitary doesn't have to send out very much tsh. Your high hcg is most likely falsely suppressing your tsh number. I assume you had you thyroid tested when you were ttc and it was normal?
If t4 is good, I wouldn't freak out. I know it's scary, but I think things are better than you are fearing they are.