Bicep pain

Last year I noticed a lump on the bottom part of my bicep near the bend in the elbow. The lump is the size of a large marble. It does not hurt to the touch. The problem is that I am getting a dull pain in that bicep. It comes and goes but is fairly regular. I also am feeling a tightness as if I just completed a set of curls. I have not been weight lifting other than occasional yard work and my 18 mth old baby boy. Any suggestions as to what this might be?