I find the more I play the more grouchy I can become, sometimes.
If I play every day, even when im not really interested, thats when I can become annoyed.
I recommend taking a break - a day if you can stomach it, and when you next play warband you might fight better and have more patience.
I have this weird thing going on with siege though, althought im not sure if it's just because weekend siege is different from weekday siege. Sometimes I can play defender for a week, and never be bothered by a "DEFEND WALL FORGET FLAG" team. Other times the smallest and stupidest stuff can annoy me.
I dont think it's limited to siege, because I played battle for a while last night and I was just playing stupidly, which of course compounds the annoyance.
Just take a break, maybe make an alt or stf and change class if you dont want to take a break. Playing as another class can make the game different, with new ways of playing and generally breaking the "same old" that can cause irritation.