Seriously on going easy. As I recall from my college bout with mono, you can do long term spleen and liver damage if you don't take care of yourself, and you seem to have a severe case, pix. Running (and any other strenuous exercise) taxes the spleen because it has to get more red blood cells into circulation to carry the extra needed oxygen--the spleen is where the extras are stored.
There's pretty much only one cure for spleen damage and that's removal; it's basically a big bag o' blood that doesn't take well to be stitched up or otherwise patched. And while you can get along without it, you don't really want to. It will tax both your ability to do any strenuous exercise and undermine your immune system. Also, if a spleen suddenly ruptures, you can end up in a life threatening situation really quickly due to blood loss.
So be nice to your spleen and do what the doctors tell you!