Pinkie mice hard actually not good for beardies. They cause liver problems in beardies. Try pheonix worms, and dubia roaches much more hutional value compared to crickets. Also try wax worms they have a good fat % so it might give them some weight. Give it some times beardies all grow at different rates. I got female at the white plains reptile expo in nov 11. She weighted only 15 grams and a few months old. After some time of giving her proper lighting anf diet, she weighed in on Sunday after a nice poop 483 grams. Beardies require a lot of protein their first 18 months, feed more insects less veggies. Offer insects 2-4 times a day, give veggies daily.
What type of lighting are you using?
What's the hot spot?
Type of substrate?