Hi! I'm so sorry- ug! I hate this early anxieties and body things that become huge stressors.
I am about 5.5 weeks and ALSO found blood this morning- in my underpants. Ug. Totally alarming and it wasn't a lot, but it was enough that I was really concerned...
I talked to a nurse who said that's totally normal and nothing to worry about unless it's a LOT of blood, or if it's accompanied with menstration-like cramping. I had cramps several days ago, but she said it's probably unrelated. She said that it commonly happens in the morning, and often happens after sex (which wasn't a factor for me, but hey).
I also have been having lower back pain- it was one of the ways I first knew I was pregnant! I get lower back pain sometimes with PMS, so I knew something was up. Maybe it's the same with you? Also, some cramping is normal as your uterus is stretching to make room for your baby, so it's something that helped me from panicking.
I hope you can at least call your midwife to get some reassurance and get her thoughts.
Lots of hugs and good luck!