They are to double every couple of days so you seem to be doing that for sure!!! Levels are hard to base singletons or twins pregnancies on....My fertility Dr. does an u/s at 5 weeks to look for the heartbeat and to see if all is well.
they confirmed twins 3 weeks ago and i have been trying to dogest it every since. I am overwhelmed and yet at the same time excited to be having more children....