How old is the quail, has it recently been moved to new ground? What do the droppings look like? The symptoms could be coccidiosis. I'm not real familiar with quail, but know they are susceptible to coccidiosis.
Treatment would be Corid (in the US, if you are somewhere else, it may be a different brand). If you think that's what it may be, then start treatment as soon as possible, treatment chart is below, use the severe outbreak dose.
Also give a oral dose in addition to the medicated water, dosing for that is here: https://www.backyardchickens.com/threads/corid-oral-drench-instructions.1211991/