If it walks like a duck... does anyone else have duck feet?

I have had 'duck feet' aka feet that turn out for my whole life. It's never bothered me overly much, occasionally I've tried to self-correct but knee pain usually results. Like I said it used to not bother me, but it seems like it interferes with my exercise. I was doing the 30 day shred and during many of the strength exercises keeping your toes straight is emphasized. During vertical lunges it probably the worst because she stresses you need to have you feet facing forward but I find this to be a very difficult task and I have to reposition myself every time I go down. As for the squats apparently pointing your toes out is 'cheating' (not something Jillian says, but I have read it online). Like I said keeping my feet straight for too long will result in knee pain. It seems like info on this is hard to find, and I don't know it there are exercises I can do to help correct it, or a way to work out around it, or if I need to throw in the towel and see a doctor.

Any input will be much appreciated!