Left forearm is swelling, warm, and tender. when straightened the pain comes from bicep down to wrist along the vein.

Should : See a doctor. Clots in the veins and infection are possibilities for your symptoms. Arm ultrasound may be needed for further evaluation.

Needs evaluation.: What you are describing could be cellulitis (skin infection), a clot in the vein in the arm (phlebitis-superficial or deep) or something related to the muscles in the arm. Regardless of the underlying problem, you need an evaluation by an md and possibly a venous ultrasound or even a ct or mri. This should be done as soon as possible.