Accutane is made to be taken with dietary fat. In fact, it's super important that you do if you want it to be absorbed. Peanut butter has fat, but you want to really get some good fat in when you take it.

https://www.acne.org/accutane.html#TakewithaHigh-fatMeal

I don't know if this will cure the nausea, but worth a shot if you aren't taking it with fat currently.

And as always, if you experience really bad symptoms, don't mess around, talk to your doc.