What Causes Nausea And Heart Flutters?

I am a 29 year old female 5'4" and 220 lbs. I am breastfeeding, I had a baby 4 months ago and after the delivery experienced severe lactose intolerance where even a sprinkle of parmasian cheese sent me running to the bathroom. My doctor suggested that I lay off of dairy and if that really was the culprit then I would feel better. He was right, those symptoms went away. That was about a month and a half ago. A couple of weeks ago I began to experience nausea. Very slightly here and there and would go away. This past week, I began having heart flutters, and now the nausea is getting worse. I checked my suger, it was normal at 108, and I have taken pregnancy tests and they are negative. Any thoughts on what this is?