I was diagnosed with mono two months ago, in February. I am recovering well, and barely have any symptoms or fatigue now. Just today, I noticed that my right armpit became painful after putting it down at my side, and that it feels swollen. When I put something in between my armpit, the pain becomes considerably less. Out of a scale of 1 to 10, my pain is about 4.5.  

If it helps, I am a bassist at my church, and play in the mornings and evenings. I have not acquired injuries of any sort in the past few days.

Is it lymphoma? ): I hope not.