Parents - Pregnancy, Babies, Baby Names, Pregnancy Calendar, Ovulation, Birth & More. that its quite normal to feel very.tired, considering your heart is pumping extra, double-work than before to accommodate to your baby's well-being. So that being said, its best to listen to your body. If you feel tired, stop whatever ure doin for awhile and take a short rest. I'm now 16weeks pregnant, and I too feel very.lethargic every now and then. I'd sit down for at least 5-10mins before resuming work.