Lumalakas and bumibilis heart rate ko

Hello momshies! New soon-to-be-mom here po. Im 4 months preggy palang. Ask ko lang po sino dito may ganitong feeling. Lumalakas and bumibilis po heart rate ko yung tipong ramdam na ramdam po sya specially pag nakahiga? weird lang kasi usually gabi ko lang nararamdaman to and pag nakahiga. I was advised by my OB to get my TSH tested. check ko lang dito if may ganitong experience and if dahil ba sa mataas na tsh to? thank you po!