My tooth in the back part of my mouth has chipped and I have to wear retainers too. Can I still wear my retainer until fixed?

The endodontist's job is to clean and instrument the canal to rid the infection and seal up the roots.  You should return to your dentist for a proper temporary restoration and treatment plan a final restorative option for the tooth.

There are times when you can feel pressure after getting temporaries.  This can be due to the temporaries being connected together and/or some swelling from the anesthetic.  Have your dentist double check that everythong is ok.  

You are likely clenching/grinding on the tooth and that is not giveng ample healing time.  The tooth gets bruised and the pain persists.  Have your dentist check that first, and if pain continues you could reevaluate the situation.  Good luck.  

The blister should be looked at by the dentist.  It could be an infection or may be there from before you had your root canal done.  There are several reasons it may be there.