Ooh I have been having strange palpitations and shortness of breath as well!
I saw the doctor this morning and she said the most likely cause, for me, is anxiety (which wouldn't be suprising given the last few months).
Even though I normally have low blood pressure, I've noticed that it, along with my pulse, shoots up when I do anything, not much, even just pottering about slowly, sys over 140 and pulse over 100.
She has taken bloods (blood count, iron and thyroid) to check them though I've had them all before and bar a low iron levels (though not anaemic) so not expecting anything to show up.
She said I could try a 24 hour tape monitor to track my heart level but I said I'd see how it went and how the bloods come back etc...
Chances are it could be anxiety related though.
Let me know how you get on x