Thyroid? Part worried talking

My dr is sending me for an added blood test to test my thyroid cuz she said that my pulse was fast and then slow and I sai what can cause that and she told me that an infection during the beginning I pregnancy can cause it, I had a bad infection that Im on amoxicillin for a couple more days but has anyone had a thyroid test and it turned out to be nothing? So far this pregnancy is so far from what it was like with my son, no throwin up, no tiredness, little crankier than usual, but completly different and then I'm now goin for this and I'm 9 weeks 3 days today and he couldn't find the heart beat on the Doppler so she thinks it may still be too early with the hand one and my office is going to try and get me an ultrasound soon to look.