trigger AccountHistoryTracker on Account (after update) {
    List<Schema.FieldSetMember> trackedFields = SObjectType.Account.FieldSets.HistoryTracking.getFields();
    if (trackedFields.isEmpty()) return;

    List<AccountHistoryTracking__c> fieldChanges = new List<AccountHistoryTracking__c>();

    List<string> apiNameList = new List<string>();

    if(Trigger.isUpdate){
        for (Account aNew : trigger.new) {

            Account aOld = trigger.oldmap.get(aNew.Id);

            for (Schema.FieldSetMember fsm : trackedFields) {

                String fieldName  = fsm.getFieldPath();
                String fieldLabel = fsm.getLabel();

                if (aNew.get(fieldName) != aOld.get(fieldName)) {

                    String oldValue = String.valueOf(aOld.get(fieldName));
                    String newValue = String.valueOf(aNew.get(fieldName));

                    AccountHistoryTracking__c aht = new AccountHistoryTracking__c();
                    aht.name         = fieldLabel;
                    aht.apiName__c   = fieldName;
                    aht.User__c      = aNew.Id;
                    aht.ChangedBy__c = UserInfo.getUserId();
                    aht.OldValue__c  = oldValue;
                    aht.NewValue__c  = newValue;
                    aht.createddate__c = system.now();

                    apiNameList.add(aht.apiName__c);
                    fieldChanges.add(aht);
                }
            }
        }
    }
    if (!fieldChanges.isEmpty()) {
        insert fieldChanges;
    }
}