Backpain on the left scapula, alrdy going for massage but not better. pain is worst when standing too long or sitting. what could be the cause?

Muscle spasm: Could be muscle spasm or cervical pinched nerve. Stretching and heat can help. If there is no improvement see a hand surgeon.

Trigger points: Pain in the midline of the back or around the shoulder blades is usually muscular. Trigger points, fairly specific areas that when pressed reproduce or trigger the pain, are common and muscular. Levator scapula syndrome is a variant near the top of the shoulder blade. Good posture, avoid looking down at computer screens. Try ice/heat, nsaid's, and salonpas hot patches.