I need some help.

I had my blood drawn on Friday and got my results today. I have taken 15 PTs and all of them are positive and just keep getting darker. my last period was May 16, and everything that I have checked says I am 4 weeks and 4 days today. The problem I'm having is that I don't understand my Serum HCG results and what they mean...my results were 18.1, but I don't understand where I fall. I have had so many miscarriages and one still born. I don't want to get excited, but this is the first time a Doctor has done the blood test. Thank you and I have added the photos for you to see.