Kevin Jepsen is having back problems

Struggling reliever Kevin Jepsen is experiencing more than growing pains. The rookie right-hander has had shooting pains in his lower back, the combination of tightness and spasms no doubt contributing to his rough trip.

Jepsen, 24, took the loss Wednesday in Seattle, when he gave up three runs and one hit and walked two in 1 1/3 innings. He took a loss Saturday against Minnesota, giving up four earned runs, three hits and three walks in two-thirds of an inning.

His earned-run average in five games: 19.29.

“It was a little sore at home, but on the first day in Seattle, in that cold weather, it locked up on me in batting practice,” Jepsen said. “I can’t get it fully loosened up, which is not allowing me to follow through and keep my pitches consistently in the strike zone.”

Jepsen’s fastball has hit 94 mph consistently, and his curve looks sharp, but he has been wild high and falling behind batters.

“It makes it tough when you’re always behind, 2-1 and 3-1,” Jepsen said. “They don’t have to look out for much.”

Jepsen has been taking muscle relaxants and receiving treatment. He wasn’t sure Sunday whether he’ll need to go on the disabled list, but he will probably be unavailable for a few days.

Into the fire

That was some big league debut for Daniel Davidson on Sunday. All the Angels left-hander did was enter a close game in the ninth inning and face Justin Morneau, the 2006 American League most valuable player, and Jason Kubel, who hit for the cycle Friday and had four hits Saturday.

“I wasn’t really that nervous until I got out there and looked around,” said Davidson, who was called up Saturday from triple-A Salt Lake. “I had to step back for a second and say, ‘You know what? It’s the same game you’ve been playing all year, your whole life. Just do what you’ve been doing.’ ”

Davidson, who converted to a submarine style at the end of 2008, got Morneau to ground out and Kubel to line out to right field. Delmon Young walked, but Davidson got Brendan Harris to fly to center field, ending the inning.

Davidson had another eye-opening experience when he discovered the Angels assigned him No. 57, former Angels closer Francisco Rodriguez’s number with the team.

“Those are some big shoes to fill,” Davidson said. “I know I don’t have to fill them, but . . . I don’t even know what to say about that. He had some good years here.”

Relief on the way?

The Angels, in an effort to add pitching depth, could turn to a familiar arm: Darren O’Day, who has been designated for assignment by the New York Mets.

O’Day, who was 0-1 with a 4.57 ERA in 30 games for the Angels last season, was a Rule 5 pick of the Mets last winter. He gave up two unearned runs and five hits in four games for the Mets.

The Angels are considering reclaiming O’Day for $25,000. O’Day ended last season with a slight tear in his throwing shoulder but chose to rehabilitate it instead of undergoing surgery.

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mike.digiovanna@latimes.com