I'm 24 weeks with DC2. Physically I've been very tired from the word go, had hoped it would improve in the second trimester but it's getting worse! Yesterday I did a bit of cleaning in the morning and it wiped me out for the rest of the day. I've just popped 10 minutes up the road to the post office and I've come home needing a lie down 
I'm not working at the moment so am lucky that I can take an afternoon nap at the same time as DS (3), which helps a lot. DH is home while the schools are off, which has been a godsend as well.
I look bigger than 24 weeks as I'm only 5'1, already using maternity pillows and so on, so I wonder if size is a factor. I don't remember being this exhausted with DS and don't fancy another 4 months of feeling like I'm already at the end of my pregnancy! Anyone else been like this?