False positive? Because this is simply impossible...?

It's possible that you conceived 5 months ago and had a period. Some women claim to have a period throughout their pregnancies. And if you gained 11 pounds that sounds about right at the 4-5 month mark. If it's your first pregnancy then you wouldn't show as early as you would if you've already had a baby. Your stomach muscles wouldn't be stretched out already so the bloated look would make sense. Best of luck to you.