Help!? Confused?

Jessica

So I found out I was pregnant on December 27 and the lines were super dark. According to my app my last period was November 17 and that would put me around eight weeks but I went to a Planned Parenthood last Thursday and they couldn’t find a baby but found a sack that was measuring five weeks two days so I called my OB freaking out I went and did my hCG levels and they are really high and they keep getting higher so why would they not see a baby?