There's a lump in my left axilla (the size of a butter bean). would an x-ray or ultrasound determine what this is?

Ultrasound: Ultrasound exam doesn't utilize radiation and is much better at detecting small soft tissue abnormalities than plain radiographs. If ultrasound does not characterize mass then ct examination with injection of intravenous contrast material, which uses xrays , can assist in characterizing the soft tissue abnormality.

Ultrasound: Ultrasound is the best modality for initial assessment of soft tissue findings, especially if they are superficial. To learn more about ultrasonography and its indications, you can read more at http://www.Conciergeradiologist.Com/ultrasound-scan.Html.