Low progesterone levels

I posted earlier today about how I was having bad cramps and spotting. Well the spotting went from brown to red so I immediately called my doctor and she pulled up my test results from the blood I left yesterday at my first appointment. She said hcg was normal at 6,000 but my progesterone level was only at a 4...she seemed worried and sent in a prescription to help raise my progesterone level. So now I'm freaking out and trying not to worry but this is my first pregnancy so I literally have no idea what's going on at this point...help!!