Yup, the pitching staff had it's share of implosions in April and May. But, as you said, the Sox were never in those games, due to a sputtering offense.
As the pitching improved, the offense (and defense, for that matter) stagnated and they started started losing close, well pitched games as well.
Look at Buchholz's record in May. He had a 3.31 ERA w/ a 1.10 WHIP
He was 1-3 that month.