Early Pregnancy Bleeding for 3 weeks

I started spotting 4 days before I got a positive test, which continued and a few days later turned into light bleeding. It wasn’t enough to fill a pad, and I went to the doctor for an exam and 48hr hcg. First draw was 182 and second was 348. Doc said it doubled appropriately and scheduled me for an ultrasound at around 8 weeks (Oct. 18). I continued to have light bleeding for about 5 days, and then brown spotting (enough that I need a liner) with occasional red/pink mixed in since then. I have a backache and some cramps, but nothing intense and they come and go. My ultrasound isn’t for another two weeks, and the wait is killing me. I feel like I’m just waiting to miscarry. This has been nothing like my first pregnancy.

I know no one can tell me what’s going on, but has anyone had a similar experience?