28 weeks pregnant always feeling weak

Alexis • Mommy to 31 week preemie twins ❤️❤️

I'm 28 weeks today and went to the cardiologist because my heart rate is around 130 while resting. They showed concerned and want to do a heart ultrasound and have me wear a monitor for 24 hours. They thing is they didn't schedule any of these until the end of the month/ beginning of September and then I don't get my results until the end of September which is about 2-3 weeks before my due date. So if there is a problem what's the point. I feel upset because I always feel like crap I can't walk up our stairs to our apartment without feeling like in going to pass out or like my heart is beating out of my chest. I see all these post about women walking around theme parks that are further along than me and I can't imagine it. I feel so tired. No one has given me any instructions just to take it easy which I do. I see my regular obgyn and my high risk dr which she is the one that recommended me going to the cardiologist. Idk what to do or feel. Simple task seem so hard