Just wanted to wish you luck hun, with my DD my levels at 5wks from lmp were only 29, I later found out at my first scan when I was supposed to be 7wks that I was only 4wks 1d when I had my first BT, I had lots of brown spotting and bright red bleeding with my DD too, not all the time but every couple of weeks for a few hours or days at a time. I had thrush and didn't know it which caused a lot of it, but I also found that it would go red when AF would have been due, and also when the cramping from her digging in got worse, though nothing ever showed up on the scans to say where I was bleeding from.

I haven't had bleeding this pregnancy, implantation or otherwise which had me worried because I've had implantation bleeding with all but my very first pregnancy, and I had lots of pain on my left side and abdominal tenderness which made me think ectopic, turns out that I have a 6cm cyst on my ovary instead.
My HCG with this pregnancy was 16 at 3wks 5d, 68 at 4wks 2d, 176 at 4wks 5d and 5240 at 5wks 5d - I had my first positive HPT at 3wks 2d but my cycles have been anywhere from 11 days to 25 days since having DD, they used to be 31-35 days prior to DD.

I have been told that as long as the levels are going up by 60% every 48 hours, or doubling every 72 hours then usually things are fine.

Sorry this is a bit rambly, just wanted to give you some hope.

I'm keeping my FXed that everything is ok and you are earlier than the doctor thinks xxx