Yes, LUMBAGOS is a Scrabble word!

Letter values in Scrabble US: L 1, U 1, M 3, B 3, A 1, G 2, O 1, S 1.

Is it a valid word?

LUMBAGOS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

backache affecting the lumbar region or lower back; can be caused by muscle strain or arthritis or vascular insufficiency or a ruptured intervertebral disc

Also: lumbar pain.