Speaking as someone who has had both...
They have similar symptoms, although glandular fever tends to affect your energy levels more than flu, and as the above poster mentioned, lasts a lot longer. Typically you might be in bed for 1-2 months at first, then your energy will steadily increase, fully recovering after 6 months/1 year. And illnesses you get during that time will be worse than it would have been, again that effect decreases over time. The glandular synptoms themselves 9ie flu-like) might recur 3 or 4 times over a year, affecting you for maybe a week. However this is about an average reaction to it - some people get off easier, and after one month feel basically ok, while some are stuck home for 6 months+, there isn't really a way of predicting that I'm afraid.
A different virus causes glandular fever (Epstein-Barr virus), and as the above poster mentioned again, it is easily detected with a blood test.
If you do have it though don't feel too bad - the worst is probably over pretty quickly, you won't be contagious for long and think of all the work you can catch up on!! (Or tv shows you can memorise!)