Dealing with anger.

I've just quite suddenly become angry/frustrated. Not sure why, except I felt frustration at my lack of progress on a project (and my personal development actually). This is not typical. I'm home alone for now, so it's not going to affect anyone else. I think I actually prefer this emotion to say, sadness. I don't feel weak when angry at least. I'm sitting with it, trying to allow it, few hours in, not shifting much. Just adding to frustration.

Advice from a IFS perspective?