Out of breath constantly!

8+4 today and I'm constantly out of breath. Even when I'm just sitting down sometimes it's like I just ran a mile. I can't even walk across the house without feeling like I need to sit down. And it's not like I'm panting or anything I just have a little trouble breathing and I feel like my heart races. I have an appointment on Monday so I'll bring it up to my doctor then but is this normal? I know your heart rate increases when you're pregnant so I was wondering if maybe that had anything to do with it? I'm not too concerned about it but it is kind of irritating because I feel like I can't do anything. Hoping it's just my body getting used to the pregnancy or something like that.