What everyone else has said. Word for word. Four is worst. By six, things will get so much better. And especially what suevv said about HG kids and clear cut answers - you probably won't get them at this point.
What we did - a sort of functional approach, all trial and error:

Cut down social stimulation. One activity a day, period.
Ramp up intellectual stimulation.
Ramp up sensory diet (google that). And time outside, in nature!
A couple rounds of OT.
Fish oil, zinc, magnesium.
A low carb, high fat high protein diet, to regulate blood sugar.
Rewards for time periods without doing hurtful things to others (yanking my hair, maniacally),
Even after we had the "it's not ASD, but..." Diagnosis,I'd still read up on ASD strategies, figuring if it looks like ASD, ASD methods must help, and they did. If it looked more like sensory issues, we did sensory stuff. And so on.
And calm down, give it time. Eval periods are stressful, don't forget to enjoy the holidays. It won't be that bad.