What Causes Shortness Of Breath?

Hi there. I previously have had 2 ectopics, 1 resulting in right tube being removed and 1 resolved with methotrexate (sp?). I am now experiencing a miscarriage (HCG level dropped from 31 on Friday to 7 yesterday). My question is, is it usual to have an uncomfortable feeling below the ribs while this is happening? I find I am unable to take large breaths of air. It's not painful as such, more of an ache.