Hey congratulations for pregnancy dear it's due to physical changes that's comes in pregnancy. So nothing 2 worry abht ..same happens to me also .I consult to my gynologist she suggest me hemoglobin nd another blood test ..nd found that my hb a low that's why feeling weakness. She suggest me iron supplements nd advised me to take rest ,healthy diet as add milk ,cheese butter,paneer,green vegetables,fresh fruits,nuts, oats ,ragi in diet ..I try it nd gets relief. U can try it dear . Take healthy diet, take rest nd go for blood test too. Take care .