My 7-week-old chihuahua puppy cries non-stop. Is she in pain?

Poor Jersey. There are so many things that could be going on. If she is eating and drinking and playing then she is likely healthy but she could be painful somewhere or having had separation anxiety. If she is crying mostly when you are away but does okay when you are holding her or near by, this is likely anxiety. You can try playing some music or the tv while you are gone to give her comfort. If she is crying all the time, refusing to eat/drink then I would be concerned something more serious is going on. Unfortunately there isn't a good over the counter pain medicine. That you can give her as most human pain meds are toxic to dogs. You can try to entice her to eat using plain chicken and rice or canned food. If she is still refusing to eat, put some honey or Karl syrup on her gums to prevent low blood sugar then take her to your vet for an exam. With her being so small I worry she may get dehydrated and malnourished. I hope this helps and she starts to feel better.