its probably because the babies have no where to move (it ususaly happens more around 30 weeks, but theres 2 so theres less room) if the doctor doesnt seem concerned then try not to worry too much, but i would make a note of it and if anything seems to be not right get it checked out

and it is NOT caused by being overweight, i am/was overweight and i could feel my daughter moving from about 19 weeks right up until i delivered (im not saying how much i weight, but its more then you lol)

Twins are usually (I don't know for sure) smaller, right? and they have less room in that crowded space. It could be because the limbs (easiest to move) are facing toward each other and not at the walls of your uterus. Also remember that they sleep alot, and sometimes just aren't very active. The only reason I could feel my baby moving at 14 weeks was becasue her feet happened to be right up against my abdomen (in what looked to be a very uncomfertable position).

It is very comferting to feel the baby move and I am sorry you are having woes over this. You might want to try drinking something sweet. (orange juice or hot chocolate) Even now, sugar will give them energy and rile them up a bit.

And just to think, when they're born, you'll probably be glad to see them sleep. (but then you can see them)

Story: When my mom was pregnate with me I didn't move for the longest time when she was in her third trimester. For weeks, actually, and she was convinced something was wrong. Obviously I'm fine. i've never been exceptionally active. I guess I was just chilling and enjoying myself for a few weeks. I kicked again eventually.