Ok so answer me this. I'm 20 weeks. I'm fit - I run or cycle most days. I'm busy and active and generally fairly energetic and feeling good. Im up and down several flights of stairs at work with no problems. But why oh why, at the end of the day when doing my single flight of stairs at home, am I puffing and panting like a 60 a day smoker and my legs feel like they won't carry me a step further?! It's just momentary and then I'm ok again, and only in the evenings. Weird.