My body feels heavy and struggles when walking, even few steps indoors. i get lightheaded, weak, and can only stand up for 5 minutes. is this a heart problem?

There are many possibilities for your symptoms, a heart issue being just one of them. You should see a cardiologist for testing to see if there is a heart issue that would explain these symptoms. There could also be a lung issue so if a heart issue is ruled out, you should see a lung doctor as well for testing. Once the issue is diagnosed, treatment can be rendered. Good luck!