please please answer me.

How do you know if you have a chemical pregnancy? What is that? 
Im afraid that im having a chemical pregnancy. No nausea or anything. 
My last perios wS march 21 and 2 days ago i took a pregnancy test came back positive and i took another one with first response and positive then i bought a digital one and it says yes. 
Am i really pregnant? Or is this a chemical pregnancy.