So I woke up this morning with pain on my left side right below my ribs, if I sit down it goes away. I got diagnosed with mono about 2 weeks ago and I'm wondering if the pain could be from my spleen, would it still hurt when I'm sitting? I also wonder if it's a muscle, I a runner and yesterday I ran further than I've been and did some other exercises, could it be from that? Why is it always something!!