Spotting NON STOP

I just found out I was pregnant last week. Went to the doctor because I thought I was just having an abnormally long period. I got blood drawn twice, and my hcg levels doubled. So seems to be progressing. I got a transvaginal ultrasound, and all they saw was an empty sac, no sign of ectopic pregnancy or anything like that. But I am now on day 18 of brown showing up on the toilet paper. I am SO WORRIED. This has been going on way too long in my mind. Has anyone else spotted for this long? Today it is heavier than it has been and I’m freaking out. No severe cramps or anything like that. Took a test this morning and it was very, very positive. Can’t stop worrying though. HELP.