Is Rapid Increase Of Beta Hcg Levels With Brown Spotting During Pregnancy Normal?

Hi I am 8 weeks pregnant tomorrow, i ve had brown spotting from weeks 5 to present, it is decreasing in amount at this time and there were a few days here and there i had none. My beta hcg were 18000 at 5 weeks, 32000 at 5 weeks 2 days, 66000 at 6 weeks and 127998 at 7 weeks 5 days. My question relates to the increase between week 6 and 7 weeks 5 days, in a 12 day span it almost doubled, what do you think? I worried it took taht long. I saw a hb of 149 at 6 weeks 4 days, but i realize with spotting, anything could happen.