My Leopard Gecko isnt eating.. is she sick??

Question
Hello, I just bought my first Leopard Gecko (a juvenile, about 6" long). I've had her for about a month and a half. For the first month she was eating crickets normally (I know because there was poop in the tank, but I've never actually seen her eat... ever!) Now, the past 2 weeks or so, she doesnt seem to be eating. Seems to be the same amount of crickets and no poop!! I tried to switch her diet.. i've given her meal worms and then some wax worms.. she wont touch them (even when she was eating the first month she wouldnt touch any worms)!!!! I change her water everyday and maintain a temp of abt 85-90 during the day and in the 70-80's in the evening. She has a moist hidebox. Her behavior seems normal- sleeping during the day and very active at night. Her tail is getting very thin which also leads me to believe she is not eating. I recently just purchased and antibiotic that is mixed w/ her drinking water as the pet store said she may have an upper respitory infection. If she doesnt, I was told the antibiotic would be preventitive. Also, In my research on leopard geckos, they should be shedding about once a month. I have no idea if she has shed at all since ive gotten her. Is it unhealthy for her to not shed for long periods if time? Overall, she seems healthy and happy- just not eating as far as I can tell. Is there anything wrong w/ her and is there such a thing as a pickey gecko since she doesnt seem to like all the things geckos typically love. Please help me.

Jamie

Answer
 Jamie, get her to a good reptile vet.  Treating with antibiotics without a veterinary license is illegal in most states and that pet shop should be up on charges.  Only a good reptile vet can make a definitive diagnosis.  If you do not have a vet yet, you can go to www.arav.org where there is a member directory by state.