I haven't flown my P3S for 3 days. Today when I went to fly it, their is a severe lag in the wifi from the iPhone to the controller which renders it pretty unusable. Any suggestions as to how to fix?
You are most likely experiencing the problems with the 3.0 update.
Please check out this post for more help on that: Extreme Lag with Go App 3.0.0
I have explained how you can downgrade your app version in that post to fix the lag problem.