What you are experiencing is typical chicken behavior. Don't beat yourself up for not quarantining. Most backyard chicken keepers don't have the space or facilities to do so anyway. To properly quarantine, you need to keep them 100'-300' apart, with the new chickens being downwind from the established flock. You need different feeding and watering stations and equipment, and should change clothes and shoes between tending to each flock (taking care of established flock first). Besides, you've already put them together, so quarantine is a moot point. One other thing to consider. Sometimes birds are carriers of disease, and don't show symptoms. You don't know they have anything until your flock is exposed.
Now that we have that covered, let's talk about how many chickens you had before adding 5 more to them. (If you mentioned it, I didn't see that) The 4 sq feet per chicken is a minimum recommendation. Integration takes some maneuvering and extra space is helpful. Can you post pictures of your coop and run? Something that is helpful in the run is to put up some hiding places. Lean plywood or pallets against the wall of the coop so a chicken can get out of sight. Leave both ends open, though, so a bird can't get trapped. Pallets on cement blocks can help, too. All flocks have a hierarchy. When a dominant bird pecks a subordinate bird, it's best if the subordinate can get out of sight of the dominant one. If they can't, the "boss" will think the other one isn't showing proper respect. Could be your 5 have no safe places to go.
How old are the chickens you added? How about the ones you already had? As long as a bird isn't being bullied to the point of blood being drawn, I'd let them work it out.
