I'm 14 weeks too (We're due the same day!!) and I still don't feel quite right. I thought the nausea was gone, but it came back, and I'm having headaches too, and just SOOOOO tired... I know the last time, I always felt worse when I was running around too much. Well, the last time, I had the luxury of crashing whenever I needed, because I didn't have a child to take care of... I just wanted to keep going despite that it wasn't good for me to do so. Now, I have DS to take care of, and I can't always crash, at least not for as long as I want, so I'm sure that's not helping.
I would guess with 6 to care for, even though your oldest are able to at least get themselves a snack if they need one, must really be hard... are you able to get a nap in anywhere?
I get depressed too, I wonder how I'm going to make it through this and if I'll ever have more children... sometimes I think this is it because I'm 37 and I felt so horrible when I was pg with DS, and it's hard now because he's so little... ugh