Super light brownish spotting.

I'm 4 weeks 3 days pregnant. I noticed spotting at 4 weeks 0 days. It's been a few days of spotting super light almost nothing at all. I have also been having slight pressure/crampy feelings every now and then nothing painful though. I took my HCG levels at 4 weeks and then took them 2 days later and they had doubled but I'm still worried! Every time I go to the bathroom I'm expecting to see a pool of blood. This is so nerve wrecking. I have a early ultrasound schedule for Friday we'll see. Anyone else have super light spotting and cramping very early in their pregnancy and go on to have a healthy baby? Thanks!