Could I have a more serious condition due to my reoccurring mono? I have had mono 5 times in the last 3 years. Each time, the symptoms get significantiy worse. I have been severely ill with mono-like symptoms for the last 3 months, but tested negatively

Something else wrong. It sounds like you have another problem. You do not get mononucleosis recurrently. I advise that you see an infectious disease specialist to get to the bottom of what 'a really wrong. Good luck.
To . To be sure, it would be reasonable to do other blood workup to be sure that you aren't anemic and don't have any other conditions. Please be seen again by your doctor for an evaluation. With mono, they probably told you this, but don't have alcohol or tylenol (acetaminophen) as your liver could get injured, and don't participate in any contact sports as your spleen will be enlarged. Keep well hydrated and eat 4-5 small meals a day to keep your energy up. If you have fevers, abdominal pain, or vomiting then you must be seen immediately.