Mononucleosis most often affects teenagers and children. That is good news, because if you get it as an adult, the symptoms can be much worse. Marcie Fraser explains.

"The older you are, the more severe your symptoms. When you get it in your mid-teens, which is the most common, symptoms are flu-like symptoms, high fever, sore throat, fatigue and can last a number of weeks,” said Dr. Jennifer Rowley, Infectious Disease Expert.

About 95 percent of adults, ages 35 to 40, have been infected by mononucleosis, otherwise known as the ‘kissing disease.’ It's spread by saliva, mucus from the throat and nose, and in some cases even from tears. Therefore kissing, sharing food or utensils can cause mononucleosis.

Once you are infected, the virus remains in your body for the rest of the life. While you cannot get full blown mono again, if your body gets run down or stressed out, the virus can be reactivated. But this time around, the symptoms are less severe.

"Reactivation of the virus that can cause fatigue, low grade fever," said Dr. Rowley.

When kids get it, the symptoms are so mild most children don't know they have it. In adults, it may take four to six weeks for the symptoms to develop.

"The typical symptoms will last three or four weeks then the convalescent phase will last a couple of months, fatigue, feeling run down, and convalescent phase for mono can be very long, sometimes up to six months to a couple of years," said Dr. Rowley.

Have mono? Don't push it, take the time to recover.

"Proper sleep, hygiene is important, adequate nutrition and slow but slow reconditioning," said Dr. Rowley.

Because mono is not treated with any medication, some people do try mega doses of vitamins to boost their immune system, this is something Dr. Rowley advises against.

"Because some of the mega vitamins are not FDA approved, and you don't know how much you are getting in a particular batch and get some toxicities and the last thing you need is a bad batch of a mega vitamin," said Dr. Rowley.