Dentist appointment and trying to fatten up!

I went to the dentist yesterday and she told me I need to clean my bottom teeth better or I'm going to be left with white squares on my brown teeth :( I thought I already was cleaning them well!  To be honest I think it's a lost cause now, they're already brown and I don't think there's anything I can do about it without getting them cleaned by the hygeinist and possibly whitened.

On a separate note, I was trying to put on weight before my surgery, but it's not going well!  I started off at 7 stone, 10 lbs, and 4 oz, then I went up to 7.11.6, so I thought it was working.  But then this morning I weighed myself and I'm down to 7.9.4!  How is this happening?!  I'm literally eating anything I want, for example last night I had pizza followed by chocolate pudding, and I'm actually losing weight?!  I'm probably one of the few people who actually wants to put on weight, and I can't!  How ironic!