What Causes The Increase In Weight And Disconcerting Heart Problems During Pregnancy?

Hi there. I am a 24 year old 5 months pregnant with my first child. For the past few weeks I have encountered many disconcerting heart related symptoms. They first started off with a rapid pulse that would come and go usually while in the earlier stages of sleep. Then I started developing palpitations which I had never felt before. My heart would have large beats that made it feel like it was coming out of my chest. I could not pin down a pattern as they would come before eating after eating etc. Last Friday I came down with the flu and had to go to the ER because my pulse would not fall below 120. They hooked me up to fluids and discharged me when it was at 108. After a day and lots of fluids my pulse came down. The next day I started feeling an irregular heart beat that did not stop. It continues even now. My pulse is lowered but the rhythm is inconsistent and I can hear it against my pillow as I try to sleep at night. My OB told me I am iron deficient anemic so I have began taking supplements but have not found relief. I see a cardiologist in 3 days but I am feeling extremely anxious and hopeless and woke up throughout the night once or twice gasping for air. I have gained the normal amount if weight and was average before pregnancy as well. What could be happening to me?