I've already filed a joint return which I need to amend. Also, found out I need to file a Form 8379. What should I do?

Why are you amending the joint return? Will you the amended return show a refund coming to you?

I found out the interest paid on my mortgage was incorrect.  Actually paid more than I first submitted. The mortgage is in my name.

The instructions for From 8379 are not very clear for your case. You certainly should file an 8379 with the amended return, the refund is not your spouses.

I would suggest that you file an 8379 by itself for the joint return, ASAP.

Then file another 8379 with the 1040X. You might want to wait to file the 1040X until the first has been processed, but I don't know if that is necessary. 

In my experience adding a 8379 (Injured Spouse Allocation) increases the processing time significantly. (The instructions say 11-14 weeks). Any errors require additional time to correct. These appears to be because the 8379 requires manual processing by a person.

I was kind of thinking it might be best to get the initial filing processed first and then worry about the amendment later.  Thanks for the help, it is much appreciated.