Miscarriages and HCG #'s

I took a preg. test at 12dpo, and got a faint positive that same day had blood work done and my quantative was only at 23 had a repeat done 3 days later it had only gone up to 31.5 the nurse told me I was going to most likely have a miscarriage the following day I started bleeding it wasn't as heavy as a reg. period, but none the less it lasted 6 days and afterwards I had brown spotting for 5 days. I started to use my fertility monitor again my first test day was cd9 it showed me a peak fertility sign I thougth that was wierd so I did a preg. test and right away within the first 30sec. it showed up positive and was much darker than any test I had taken before the bleeding. I called my OB they said come down for some more bloodwork to make sure my levels were going down the way they should. I got my results today they went up to 431. They sent me for some more lab work today I won't get those results until tomorrow. What could be going on? Is it normal for your #'s to go up that much after you miscarry? Any advice would be greatly appreciated!