I created one content typa and I put one fieldset group through Field_group module, but I can't see settings to add more fieldset. I've 6 fields per fieldset. But I'm not able to do the same with fieldset. It can be done with particular field only.
You can add more fieldset by Add new group option available in Manage field page, please find the below screenshot..
And you can drag and drop the filed inside the fieldset as you required