I am so sorry that I am not living in your country, because then I would have done everything to help you get the support you need.
Yes, your symptoms are stress-related. Your physical body is expressing your spiritual state, and I get a sense of you feeling trapped.
You need to ask for help. There are people around you who are able and willing to help you, but if you do not ask for help, everyone will think that you are coping.
You indicate that you take your grand-parents to see the doctor. How about asking the doctor for the details of organizations that can provide assistance? And when you do get some relief, insist on using the time that is freed up for yourself and for what you need, even if it means leaving the house to sit somewhere and do nothing.
You are giving all your time and energy to your grand-parents and there is nothing noble about it, no matter what other people tell you. It is hard work and you are quite right, you have a right to your own life.
Let's look at ways for you to relax. You need to learn about meditation. On my website you can download a free meditation and instructions on how to meditate.
And this may sound funny, but please try it. I want you to take ten deep breaths in every hour - as deep as you can, and then blow all that breath out again. When you get as stressed as you are, you forget to do something as simple as breathing.
You should also insist that other family members such as your mother do their share in terms of looking after your grandparents.
They are not your responsibility and you do not need to continue to sacrifice. Once you have made that decision to put yourself first, you will discover how many people are ready to help you. Then you need to accept that help - and that may be the difficult part.