About Three To Four Weeks Ago I Started Getting Acute

About three to four weeks ago I started getting acute extreme pain across the top of my right big toe. The attacks come without warning and without any common cause. (with shoes or without, exercising or at rest, doesn't seem to matter) I may have several attacks in a day or none at all for a day or more. The pain is excruciating (make you feel like your knees are going to buckle kind) but only last 5-10 seconds. If I push on the top of my toe right behind the nail and in front of the joint the pain immediately subsides. I am not aware of any injuries but this did start after walking in very soft sand dunes for several hours without shoes.