you might have just been sharing a drink with someone when you caught it, and you might be re-getting it though the same person? cause it can lay dormant in someones body for (don't quote me, not a doctor) months.
there isn't much you can do about it once you have it (except aiding the symptoms ie. ibuprofen for muscle aches) but anything that lowers your immune system, stress, lack of sleep, unbalanced diet, will make you more susceptible to it. my roomate gets it sometimes when he works too much =/