Patience....why does it come and go?

I have two classes that i'm responsible for teaching writing and math. I have my class in the morning for 40 minutes, another class for the next 130 minutes, then my class again at the end of the day for another 90. I never have patience with my class. I seem to always, no matter what have patience with my large blocked class! That class has 5 non-English speaking children in it too! I just feel that i'm totally wasting and hurting my class' learning bc i get so frustrated with them at times. I know its Friday and I want to leave, but man....i hate feeling anxious and guilty for not teaching to the best of my ability! PLease Lord, HIT ME! Yesterday was so great...why am i so anxious today? I want to be patient, but i have so much for them to learn. I know i can't just throw the lessons at them and expect them to know it...but sometimes i just can't reach them. i put my teaching at a high standard, therefore i have high standards for EVERY kid. THis job is so rewarding at times and soooooooooooo frustrating at others. At least i have 23 healthy, happy, loving kids...that's a good thought. i'm blessed...besides, i'm going to PERU! I am going to do it. Its so much better putting my feelings down on this, it helps me reflect on what i really have, not just focus on the negative. sweet :)