Is it a tumor?

As further info, i have had two ganglion cysts on my wrist and also have an angiomyolipoma tumor on my kidney (benign).  I felt this pain in my forearm like i had done something very strenuous and it was hurting.  However, i had not done anything unusual.  I began to feel around and it seems there is a lump; however, it seems elongated.  Unless it is just my muscle.  If it is a muscle, it is larger than the one on my left arm and I can move it sort of side to side.  It is not easily visible as it is under the skin; however, i can tell that this side looks a bit different from my other arm.  Is this anything to be concerned about or get checked out?

Thank you and warm regards,

Judy