Isaiah 26:3 "Thou wilt keep him in perfect peace, whose mind is stayed on thee: because he trusteth in thee."
It think sometimes we just expect that we are supposed to have peace and joy all the time because we are Christians. That somehow, we get saved and all of a sudden we can go through problems calmly and easily without blowing up all the time. The the peace that God promises doesn't come after we get a free ticket and now we have it forever. It doesn't even last all day when we read our Bible in the morning, but when we have that clear line of communication with God throughout the day and our mind is "stayed" on Him. That's why I love to choose a verse out of my devo's in the morning that I take throughout the day, because later, when I think about that verse, I don't just say it in my mind, but I go even deeper in my thoughts than I had in my devotions that morning. So I encourage you to do the same, and even go on long rabbit-trails in your thoughts. It helps keep your mind on Him, and it does give you the peace and wisdom to get past your own lack of peace during the little trials we all have in every day.