I had extreme pressure in my head and left side after running?!

I ran a half mile, then stopped for about one minute, then ran a quarter mile, stopped for about 30 seconds, then ran another quarter mile. After, i got extreme pressure in my head, similar to the feeling you get when you are driving in a high altitude area, then descend quickly, but a lot worse. I also got a very bad cramp- like pain right under my ribs on my left side. I have mono, the symptoms stopped about one month ago, but i heard it can damage the spleen, which is right under the ribs on the left side. Just wondering if its related to mono, or what. I haven't been healthy lately so i want to be safe. Any advice helps! Thanks!