According to Mark Prior and the Cubs, there?s nothing mysterious going on with him, either with any illness or rumored injury. The Cubs have put Prior on a gradual throwing program in an effort to avoid a recurrence of the elbow problems he experienced the past two spring trainings. Prior spent early January getting over a nasty upper-respiratory bug. ?Sick enough to go the E.R.,? he said Saturday, referring to a hospital emergency room back home in San Diego. ?One morning I woke up and I couldn?t swallow or breathe very well, so that?s why they rushed me to the E.R. I was down for about two weeks, so I?m just behind.? Prior said he?s on a ?structured throwing program,? and that he expects to pitch in one of the first games of the regular season. The Cubs have him penciled in to throw in one of the first three or four Cactus League games. ?I?m throwing; I feel good throwing; I?m just behind,? Prior said.