What Causes Bloating/pain In Abdomen While Having Occasional Palpitations?

Hi, I'm a 30 yr old female & for the last 5 months I've had occasional palpitations, almost always in the evening and while at rest, usually in bed. I've had an ECG & bloodtests which showed nothing. The last 2 weeks the palpitations have become more like 'heart hiccups' but are much more frequent. In the same amount of time my abdomen has become very bloated (not hard or tight, just bigger and uncomfortable), which I initially put down to PMS, as I'm due my period, but now I seem to have a constant, mild but niggling pain in my upper left abdomen, right under my ribs. Are these symptoms related? Or if my heart has nothing to do with it, what could be causing my stomach pain? No nausea or vomiting, it's just been there for what seems like a very long time..