Lump in my arm around the bicep?

i have a small, oval-shaped lump on the inner part of my upper arm close to the elbow. doctors have taken a look at it and took an ultrasound. the ultrasound showed that it was not a vein (so not a clot) and most likely not a cyst. they told me to come back in a week for an MRI if it doesn't subside. they told me it could be a swollen lymph node. oh and by the way, i'm a leukemia survivor and had a bone marrow transplant 3 months ago.