You should be feeding him/her 3 times a day for 10-15 mins at a time, as many as they will eat in that time. 20 crickets is no where near enough. Havoc was eating 100 or so a day when he was a baby.
normally with a baby bearded dragon you want to try feeding it 2-3x a day as much as it will eat in 15 mins. but not all bearded dragons will eat like that. my bearded dragon who is nearly 5 months old just gets a dish of calci worms and small dubia roaches put in her viv in the morning and she eats when she wants to.
i dont count how much she eats, but depending on how hungry she is she can easily eat 100 large calci worms and 50 small dubia roaches