With your presentation i think you should seek for medical attention with a gynobs + internist. It might that you are having pulmonary embolism
or heart failure
since you are a known hypertensive and now you are pregnant. With all your previous medical conditions it is better you seek medical attention now for your sake and the sake of your unborn child.
As you rightly suggested, given the age of pregnancy
, it is possible that as the baby is growing, your diaphragm is being compressed upward and consequently your lungs, so reducing the surface for gas exchange. Normally, nature has regulated all of that, and made it in such a way that this would not happen (but does not cancel the fact that it can happen.
Consult as soon as you can.