dI thought I'd chime in with my experience. When I had mono, my Doc (who is also my Uncle and was rated one of the best in the state recently, so he knows what hes talking about) told me that generally there are two manifestations of the disease.
Personally, I got it really bad, throat swollen so I couldnt eat (had trouble breathing too), etc etc. I was on prednisone for 12 days, during which time I lost 15 lbs, most of it muscle (I went from benching 225x13-14 to x6 in about 15 days). However, my body returned to normal and I lost all symptoms (most notably the extreme lethargy) within 3 weeks of diagnosis.
The other general manifestation is the slow, gradual buildup in which people have the time to run themselves down. One of my friends got it this way. He didnt get the bad sore throat or really bad swollen lymph nodes, and played through an entire baseball season without knowing. By the time school ended and he got an official diagnosis, he had had it for around 2 months. It took him a good 6 months to rid himself of the tiredness and general symptoms youve described.
Although my case was short lived and quite extreme, it served me best because I did not end up pushing myself too hard. The majority of times you hear people really screwing themselves over with mono is when they get it like my friend; all the symptoms are not severe enough to warrant any immediate attention. They dont see the symptoms real bad and overdo it, prolonging the illness for months.
My best advice is to just rest like you are doing. Although you might hate what it is going to do/is doing to your body, if you try to work out and overexert yourself (which isnt hard with mono) you will just prolong it.
