New Betta

Question
Ok so I have a 37 gallon tank with a Molly, guppie, angel, plecostomis, and some bamboo shrimp. I have had the tank for about 2 months now, finally getting the ammonia to stay at 0. I just bought a betta today from petco they had him in a tank with other fish so I was surprised because I thought Bettas always had to be kept seperate from other fish. But at the store he was just hanging out with the others, so the guy said I could put him in with my fish. So I got him home, acclimated the water before adding the betta, and he seemed to be doing well with my fish, my Molly is a little bit aggressive toward the betta which surprised me. Anyways my betta has just been hiding in the tree I have, and now just laying on the gravel at bottom of aquarium, he gets up every now and then and swims around. But if he's not swimming he's either lying on gravel, or wrapping his body onto plants and stuff??? What should I do I don't want him to die already, he's soo pretty!!

Answer
Elicia,
If any of the Guppies are male, I would remove the Betta right away. Mollies and Betta's don't usually get along well. Male Betta's should be kept alone in their own 5 gallon tank with a heater. He could just be getting used to his new home, and sometimes it takes a few days. Make sure he is not being bullied and that the tank heater is set at 80 degrees, and he should be ok in a few days.