It's part of parenting!

Well it happens on occasion, I do all I can to make sure that my boys get the very best care from me.  But every once in a while I lose control.  I get a splitting headache because nothing I do seems to help Ashton.  I do everything that I can to make him better or calm, but nothing helps!  My head is aching my eyes hurt and then I lose my temper! I think it's normal to lose control over screaming kids sometimes.  But my delima is what do I do when I lose control with an Autistic child?  How do I calm myself fast enough that I don't take it out on him.  I won't hit him out of anger or anything but I yell and scream sometimes! I can't stop myself at times.  I find myself getting red and hot from anger because he just won't stop.  What next?  How do I handle this?  Is it wrong to yell at him or get angry?  I understand that some of his problem is just who he is but still I can't stop myself from getting mad somedays!  I feel so horrible when I lash out at him like that! He is after all just a baby!  Does it make me a bad parent to yell at my autistic son?