How do you know when your spleen has been ruptured?

I had mono (or glandular fever) symptoms in the last week of May, and today I've started to feel pressure behind my left rib cage where my spleen is. I walk a around a lot, but I don't want to do any strenuous work for a few more weeks because I don't want to rupture my spleen. But could it already be ruptured? Right now, it feels like my spleen has expanded a lot.