Did anyone else normally lose weight during pregnancy?

I'm curious about whether it is normal to lose weight during pregnancy. I lost 45 pounds while pregnant with my 2 yr old, but thought that it was due to a bad gall bladder. I am now 20 weeks pregnant with my 2nd (do not have a gall bladder anymore) and do not eat any differently or healthier than I ever have and so far I've lost a total of 12 pounds. (I haven't had bad morning sickness or anything, sick to my stomach and thrown up a few times but nothing severe). It seems weird and everyone says that I'm weird or disgusting or things like that to tease. I am not a small person so it suits me fine that I lose during pregnancy rather than gain, and my doctor hasn't said much about it other than to make sure that I am healthy and not dieting or anything but other than that doesn't act like it's a big deal. Has anyone else had this "problem" and did you find any reasons that may have caused it? I go back tomorrow to the doc and am quite curious to see if I've lost anymore, and as long as the baby is growing and healthy it will be just fine with me =)