continued episodic left side-spleen?-pain

My teenager was diagnosed with what was thought to be a mild case of mono in August of 2010. However, she experienced a horrible sore throat, delirium, and broke out in a rash twice to her arms (? drug reaction) and then had some left-sided tenderness. Since then she has had 2 episodes of excruciating left upper abdominal pain in the splenic area. This last time I took her to the doctor and all tests came back negative. They felt that it was not related to the mono's effect on her spleen but many of these sites say otherwise. She did engage in some exercise soon around the time of the pain worsening (it was already there beforehand). What can we do? We want to try and prevent this again if possible!