Weight Gain?

Sooo, I think I am starting to get my appetite back! But I still can't gain any weight! I know I've mentioned this before, but, why can't I have this problem when I'm NOT pregnant?!?! Anyways, on Friday, I was pretty proud of myself. I ate great all day...I had an Ensure Healthy Mom shake for breakfast, and then went to my parent's house and had a piece of homemade apple pie. For lunch I had some rotisserie chicken and for snack I had an energy bar. Then for dinner I had a bean tostada with sour cream and guac, and a before bed snack of a powder and milk nutrition shake. So, the next morning...I lost a whole pound! Then yesterday, I ate well again...I even had 3 pieces of pizza for dinner! And this morning...same weight! So, I've lost a total of 9.5 pounds! I know the weight will start stacking on soon enough, but I actually feel bad to loose so much. I know I am safe if I don't loose more than 10% of my original weight, so I still have some room. Can I say it again?...why can't I have this problem when I'm NOT pregnant?!?!