Beta questions in week 5

I just got beta hcg results back, and they did not double even though 62 hours had passed.

At week 5, day 1 (21 days post ovulation), my beta was 2532. 62 hours later, at week 5 day 3, my beta was 4341.

I’m worried because I’ve had a lot of spotting every single day since the day of my missed period, and, I had some really sharp pain in my pelvic area last weekend. I have an ultrasound scheduled for next week, and wow, is the waiting unpleasant.