I had a pilonidal sinus nearly healed. Then the whole thing opened up. Why? This thing is driving me crazy. I will get brain damage before this heals.

Not uncommon. Don't get discouraged it is a common problem in some almost heals and breaks down as you described . Keep the ares clean , take regular showers wash the area with soap and water ,happy dressings go for follow up visits and be patient for couple of wks . It will heal.