Translation:My friend did not come to school on Wednesday because he had a headache.
When using потому что there isn't supposed to be a comma between the two words. When the sentence is machine-read, there's a long pause.
Maybe this is a really dull question, but why is "был/о" not necessary to express that he HAD a headache? Why is it that without it the translation isn't "has"(present)? Obviously it wouldnt make sense with the context, but I thought that without a form of был ownership was still present tense?