30 yeaes old. Have pea size lump on big vein in my neck. Tender to the touch. What could it be. I get them in my groin area to but those are painless.

Lymph. This may be a lymph node which is tender because it formed acutely. If it doesn't recede after a week or if it continually enlarges or if a cluster of them appear, have your physician examine you. He/she will order any appropriate tests.