i was hit in te chest with air-bag in auto accident. i developed a racing pulse and swollen lower legs. it was heart failure caused by atrial flutter.
Have you discussed this with your doc? I'm not to knowledgeable in the "expecting" area but "the high pulse/low bp" does ring a bell, but I'm not sure what. I've done a lot a research for my own issues and it seems as though I remember coming across that particular symptom but I don't remember what it meant. I'd post in the pregnancy forum to see if you can get a better response.
It sounds like it may be POTS - postural orthostatic tachcardia syndrome. Does your heart race when you stand up and are you dizzy ?
Whatever it is, you do need to see your physician.