My 9lb havanese seems to scratch like crazy with the warm weather as she had the behavior last summer. Help?

Her body temperature is also warmer at this time and she pants like crazy, despite the fact that she is in a 72* air conditioned home and has plenty of water to drink. Perhaps allergies or the heat? What can I do? Last year I paid nearly $200 to a vet who ended up just giving her an antihistamine shot.