I'm exhausted from having to keep apologizing to someone every time, because of frequent troubling behavior or not keeping up with group activities.

That feeling is only natural—you're already trying hard enough. In common: being worn out by apologizing is also a sign that parents easily become isolated. You don't have to carry it all alone. Sharing the behavior's background with the preschool/school and thinking of measures as a team can reduce the very situations that call for apology. Connecting with parents in the same position can lighten the feeling too. What the family decides: how far to apologize or explain is yours to choose, by situation and person. Your exhaustion isn't weakness. First rest yourself, and lean on support.