Why is my dough not very stretchy?
you aren't letting it rest long enough....When I used to ruin (run, i meant run, but ruin is just too funny so I am leaving it there) a pizza restaurant, if you forgot to prep the dough the night before and allowed the dough to rest in the refer over night, the dough would be very stiff and springy....

In your case, without really knowing your recipes and so this is a stab in the dark, you probably just need to let the dough rest at room temp for 30 minutes.