Fluid around heart?

Hi, I recently went to the doctor, because I felt like I had a cold (which turned out to be the flu) and I wanted to know if it was serious. Here are my current symptoms:

- Sore throat (2 days ago but past)
- Coughing
- Runny nose
- Fever at night (cannot sleep)
- Fatigue during the day
- Shortness of breath (hard to breathe sometimes)
- Congested ears
- A little dizziness

I feel like coughing because it feels like there is some type of fluid/mucus build up in my throat, and I want to get rid of it. It's hard to go to university during the day when all I want to do is sleep. My current symptoms have been reduced to runny nose and slight coughing.

and here's the basis of what he said to me, after listening to my heart, looking into my throat and ears, and listening to my breathing:

"I'm not trying to scare you, but I can hear some fluid build-up around your heart, and so its important for you not to exercise for the next few weeks until your body is completely better. (which is around a month) So, even if you are overall feeling better, and even if your symptoms are gone, it takes at least 30 days for the actual flu to go away.  Take these Tramacets with Advil to boost your immune system to make the flu go away."

So... what exactly is wrong with me? I am very, very confused. I'd like to know why the fluid build-up was brought up with the flu symptoms. Are they related? Or, do I have something more serious than I think?