I've had constant shortness of breath for the past few days- at the end of each breath it feels a bit shallow/hurts.i have no cough/cold possible causes?

Do not wait: Breathing trouble maybe a sign of blood clots in the lungs. Check with your doc ASAP. This could be a very serious and life threatening problem. It also could be early asthma which is easy to fix. BUT PLEASE DO NOT WAIT AND CHECK WITH YOUR DOC.

PutAHolterOnYerDimer: If you have pain in one area of the chest when you breathe in or out, along with that sense of not getting enough air, I'd suggest you see a doctor who could get more details and also examine you and then decide what, if any,tests he might want to do. I see here that you've had a Holter and a D-dimer done in the past, so why not contact that doctor. I suspect (s)he' would know you fairly well.