Why wont my Baby Bearded Dragon poop?

My Bearded dragon is maybe about a couple months old (pet store, it was Petco, didnt know how old exactly) I bought it on tuesday, june 14, 2011. I have two 60 watt bulbs for the aquraium, aquired a UVB light, so the lightings fine. I have a 20-25 gallon tank. I feed it 2 crickets a day, their about the same distance between its eyes, maybe a little bit bigger. I feed Izzy (my bd) lettuce when ever shell eat it, tried broccli, she didnt like it much. The aquarium is lined with repti sand, she has a basking rock, and a hiding place. she has a water bowl. She was scared of the crickets at first but ate them with time(took her about 15-30 minutes to eat just 1) She's about 2 and a half, maybe 3 inches from head to the beginning of her tail, her tails about 3, close to 3 and a half inches long. She pooped just before we fed her 2 days ago. But hasnt since. There was a tip that if i let her lay in some warm water for 10 minutes then shell poop, im trying that now. She didnt poop in the water and i just put her back in the tank. She went to her basking rock and is, well, basking. Im worried that there is something wrong with her.Any tips????!?!?!?!