I can certainly relate to your post as I could have written it last month about our Chinese water dragon. The first week we attributed it to relocation stress but then he started to lose weight and became so lethargic he wasn't moving from wherever I placed him, so to the vet we went. We went over his setup in detail, no problems there. However, the fecal test revealed a really high infestation with parasites and blood in his poop. She was brutally honest in that, as she said, she didn't love what she was seeing. When I told her we'd only had him 2 weeks and where I got him, she wasn't surprised. She did tell me that she and several other exotic vets here have written to Petsmart's breeders numerous times regarding all the parasite-laden reptiles brought in by their customers and urging them to do something about the suppliers they are using. We gave the water dragon metrinidazole and carnivore care but he was just beyond saving.
I spoke to the manager immediately after the visit so he was aware of what was happening and gave him a copy of the vet's report. When the poor thing died, I informed them of that as well. They refunded what I paid for the dragon, paid the vet bill, and refunded tank and lights, etc. While I wasn't impressed with what that poor little dragon went through, Petsmart stepped up as they should and I'm glad.
My advice is to immediately have a long talk with store management. They have their 2 week guarantee. In our case, the water dragon died several days past the 2 weeks but they honored it anyway. It was a stressful situation here emotionally, especially having to force feed meds and supplements and watching him continue to decline, even though the vet's opinion was that he likely wouldn't make it.
So, my heart goes out to you. I know exactly what you're going through and wish you the best. Let us know how you're doing.