If you are not showing your dog, it's not so much what they weigh as their body condition that matters. Chihuahuas can weigh anywhere from 2-15 lbs. size actually does not breed true in chihuahuas. 15lb dogs can have 3 lb pups and vice versa. As long as your dog looks healthy, has a visible waist and has ribs that can just be felt when petting the dog, with no hip points showing unless the dog is very young, you are just OK. all three of mine hover between 6.5 and 8lbs. They are larger examples of the breed. We used to joke that half of foxxy's weight was fur, but she really was a very solid dog, stockier and well muscled.
we don't pick up our dogs much unless we are ourselves being lazy, and they have to climb 3 flights of stairs just to go potty, so they stay very trim. But they're still about 7lbs give or take a few ounces