Hi.
It's been six months. Honestly, I think unless your grandmother is blind, she actually already knows or at least has a hint of your situation. She's still a woman after all.
Please go to a doctor. Do it for yourself and especially for the baby. You seem to have decided to keep the baby since you are in your present situation but make sure that your keeping the baby is done with a lot of physical care as well as emotional care. Right now, I am a believer that your baby can sense your present emotions and will be suffering along with you. THe moment you relieve some of that depression, your baby will be relieved as well.
I never got to tell my grandparents when I got my wife (who wasn't my wife then) pregnant. I told my mom as soon as I could but it took five more months before I could tell my dad. I didn't even tell him face to fact though we were living in the same house. I wrote him a letter. I told myself that if I came home that day with my stuff dumped on our front yard, then I knew the answer. The answer wasn't at all like that. My dad came to me when I slept that night and I saw him crying as he asked me why I was trying to bear this alone. The next day, as I left for work, he again told me the same thing and assured me that we would work together to deal with this.
GIve your parents and grandparents a chance to help you. Yes, they may throw an incredible fit when they first find out but that's what happens when people are surpirsed. The usual first emotion they grab is one of anger. Sooner or later, they will calm down. Look, your grandparents allowed you in their house and accepted you. I very much think that they will also accept you and your baby. They will be disappointed especially when they find out that not only did you make the same mistake but that everybody in the school knows but they didn't.
I guess what hurts a lot is that they weren't able to help you, that your life will be harder (your life is not over and never believe that it is) and that you found it so hard to tell them.
The best thing to do is to tell the grandparent who can either handle it better or you fell closer to. BEtter if that's the same person. Once you get that one person, you can then plan out how you'll tell everyone else. Be storng and pray a lot. You'll need God's help now more than ever.
Erick