I have a female Min Pin who is 1 year and 9 months old. She has been whimpering and constantly crying since yesterday. I have gave her food and rubbed her belly but she still is constantly whimpering.

This is a hard one to answer, whimpering is often a sign of discomfort or pain, but unfortunately dogs can't tell us what or where it is hurting which is why we have vets to run tests to determine the cause.

Does she spin around or lick any specific part of her body that might give you an indication of where she is in pain?
Why did you rub her belly, do you think that might be the cause?

Do you think it might be a behavior problem? If so how is she acting apart from whimpering, does she try to hide or seem skittish at all? Has anything happened around the house that might have upset her?