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Create an object called AccountHistoryTracking and fields like APIName__c,OldValue__c,NewValue__c then create a fieldset on Account called'HistoryTracking' with the fields you want to track on Account and then write below code to track history on account.This way you don't need to worry about history tracking limit per object.

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));
if (oldValue != null && oldValue.length()>255) oldValue = oldValue.substring(0,255);
 if (newValue != null && newValue.length()>255) newValue = newValue.substring(0,255); 

 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;

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