Slight chest pressure...?

Hi.. Last Saturday my chest was tight and I felt like I couldn't breathe (Which I could, it was just my imagination telling me I couldn't breathe) and ever since I'm been thinking about it.. And I always think my chest is tight again and I can't breathe. But lately I haven't been thinking about it and the feelings completely went away. Now I have a slight pressure on my chest, but I can still breathe and get deep breaths. I don't have any pains or anything else, just the small amout of pressure. I've been stressed a tad bit, and I think thats a cause. Plus the vents in our house are blowing up dust from underneath the house, and we are going to get that fixed. I'm a healthy twelve year old girl who shouldn't be experiencing these problems.. Can anyone maybe diagnose something? I think its just stress, but... And don't try to scare me, either. That will really make me feel like I'm dying.