Aih, 39 weeks tu memang exhausting, auntie, your body dah kerja keras support the baby, plus the extra weight and hormones memang bikin drained je, bukan sebab umur (I know a few mums in their 40s yang deliver fine, energetic jugak). Weak feeling at this stage is pretty normal, tapi since you're having trouble sleeping and feeling very weak, I'd suggest mention it to your doctor or midwife next visit, bisa jadi iron levels, blood pressure, or something simple yang boleh dibantu, takpe just to be safe. In the meantime rest as much as you can, makan nutrient-dense food, and try gentle walks kalau boleh, sikit-sikit pun okay. Hang in there, dah dekat dah!