You are still doing a great job by providing care for you grandparents. I am myself doing the same, albeit for my parents. I myself went through some of these feelings sometime ago. Let me just tell you what I did to overcome them and hope it can help you.
  1. Meditate
  2. Explore within for what you want from your life.
  3. Start involving yourself in some other work like gardening, pet caring, cooking etc. Be busy.
  4. Get together with people on a daily basis.
  5. I started teaching neighborhood kids and adults 'How to speak in English'.
Hope it might help you out....