Well, sounds like you count your dpo as the day you had the iui. Your numbers are doubling like they should, I wouldn't think it would be multiples though, they look normal. I've also heard that women pregnant with second child or more tend to show faster than the first pregnancy, so that could be why your pants are fitting tighter, also iui does carry the possibility of multiples. You'll just have to wait until your first u/s to find out. Last, don't assume this pregnancy has the exaxt same symptoms as the first, each pregnancy is different even with the same woman, lots of women on here will vouch for that. Good luck and congrats on your pregnancy!
Thanks for the info! I know it's crazy, but you know how sometimes you just have a feeling? When I went in for my ultrasound to check my follies bfore the iui I had two that were 23 mm and I could feel I was ovulating the same day I had my iui and then 8 days later I had a sharp pain in my uterus area and then the next day I had the same exact pain on the other side of my uterus. Who knows? I know sometimes our imagination gets the best of us. I'll find out Wednesday!
My HCG - levels were 112 DPO 13 (if I remember correctly )and 337 DPO 15 (I'm sure of this one) and I had twins. My friend had already 750 DPO13, so you never know... Good luck!