Dog has excessive drinking and panting?

My beagle/staffy crossbreed is starving hungry all the time. She always has been a little inclined that way but seems more desperate now and eats tissues and hankies and paper including lotto tickets and never rests in her search for food in the house. She is overweight and we're trying to help this by giving her 3 small meals a day of steamed chicken mixed with steamed vegetables and brown rice. She pants LOUDLY all of the time...even when she's asleep sometimes and we've noticed that she is drinking ecessive amounts of water. She went to the vet about 3 weeks ago with vomiting and an extremely high temperature and had an antibiotic for a week. She is 10 years old and this was her first visit to the vet since her vaccinations years ago. Any ideas?