Dear Anita,
If no one else is saying this to you, then let me say it:: Thank you for stepping up and taking care of your grandkids. Even if it is for just on a temporary basis, you are making a tremendous difference in their lives.
In my state (Pennsylvania), you would be paid as a foster parent, even though you are a blood relation. Are you receiving payments in your state for the care you're providing? If not, then you might consider confering with Legal Aid or some other legal advisory group to obtain information on your rights as a grandparent and to help you advocate for receiving proper support from the state. Caring for your grandchildren shouldn't impoverish you.
Two other suggestions: Can other family members (from either side of the family) help defray some of your costs? Is there a local church group that would consider providing you with some support to continue doing your good and vital work?
One way or another, I hope you are rewarded for doing the right though difficult thing for your grandkids.--Barry Jacobs, co-author of AARP Meditations for Caregivers