Mono or Lymphoma

I'm 40  yrs old and very active (runner) and healthy. I've been sick w/a high fever, one sided sore throat, swollen face for over a week now.  The dr. initially prescribed antiobiotics, but they did not work so they suspected mono and took blood.  The dr. said the test was positive for mono and that also my liver enzymes were very high and platelet count very low (not life threateningly low, but low).  I was ok with that, but then did some reading and tied in some other symptoms I was having prior to the fever.  I've been having mild trouble swallowing for the last yr or so and if feels like I have something stuck in my throat.  I have had heartburn for the last couple of months.  Also, I run and my chest has felt tight (mildly) while running and I've developed a cough when I run  mainly because I feel like something is stuck in my throat and I'm not getting enough air.  I just discounted those symptoms because they were mild enough and planned on bringing them up at my next yearly physical. However now,  I've never ever felt this sick before in my life.  I just have no energy whatsoever and the fever will not subside.  
I intend to call my dr tomorrow w/questions, but in the meantime I am rather freaked out.  My brother passed away from leukemia 15yrs ago, so I am concerned for myself.

Is it possible to test positive for mono if in fact I have lymphoma?  
What is the likelihood that I never contracted mono before.  I come from a large family (7 kids) and 2 of my brothers had mono when I was growing up.

I'm just really concerned this is something more than mono - am I way off base?

Thank you!