20 weeks pregnant, three days i've feeling like i've been running randomly, even though i'm laying down and it's hard to breathe. 100 pulse. normal?

Yes, within normal: At 20 weeks pregnant you are halfway in - your body is bathed in progesterone, your blood vessels are dilated pretty much around the clock (as they would be if you were exercising). Pregnancy is a lot of work on the heart - but staying at 100 beats/minute round the clock is also not idea. If you haven't been check before this for lung or heart disease, may need to be in order to tease out