Scared I'm having another miscarriage

I had a miscarriage 6 months ago in February. It took 2 D&C;'s to clear it out. August 9th I got a positive test and have had several positive tests since. According to my last cycle my edd is April 21 putting me at 5 weeks 3 days today. This past weekend I started spotting. It was brown and cramping to go along. I freaked out. It slowed down a good bit and I calmed down a little after talking to the dr. But Monday afternoon I went to the bathroom and saw bright red. I got home and my husband left work and took me to the ER. Urine test showed a positive pregnancy test, blood draw shows my beta hCg at 300 and according to dr it's low for 5 weeks. They did a transvaginal ultrasound and where as my uterine lining was a little thick but there wasn't a visible pregnancy.

The thoughts are either I'm having another miscarriage, I'm just too early yet, or it's an ectopic pregnancy. I go Thursday for a new blood draw and dr follow up.