The Mystery

The mystery:

Cory has had these bumps on and off for several months now.

They'll come, generally (but not always) right after playing outside. Obviously they are pretty itchy. They only last for about a half hour, and then disappear completely.

I took him to the doc, who said it was scabies (a mite which is usually cleared up after one treatment), but these pics were taken the day after treatment.

He gets them on his legs too, and then scratches them, leaving a bunch of little scabs all over his legs.

Does anyone have any ideas what this could be? I'm thinking some kind of allergic reaction to the grass or something. If so, do I need to take him back to the doc? I feel silly taking him in for something that comes and goes so quickly, but it's been happening for so long, ughh. Wishing kids came with an instruction manual...