MILWAUKEE — In remembrance of an iconic sitcom set in this city, these are “Unhappy Days” for the Mets.

Their season may have jumped the shark Sunday, when starting pitcher Jason Vargas departed with “mild” left hamstring tightness and a makeshift lineup stagnated.

And after the Mets’ 3-2 loss to the Brewers at Miller Park there was a further development to potentially impact the team’s rotation: Manager Mickey Callaway announced Steven Matz was returning to New York to have his left forearm examined because of a nerve issue.

At least this latest Mets loss — which completed the Brewers’ three-game sweep — took only nine innings. It came a day after the teams played 18 innings, with the Mets losing on Ryan Braun’s two-run single against Chris Flexen.

“We want to right the ship as soon as possible, but that is not something a bunch of stress and worry is going to help with,” said Brandon Nimmo, who went hitless in three at-bats and extended his drought to 0-for-25. “The best we can do is try to treat this as normal as possible and let guys go with the ebbs and flows of the season. If everybody starts panicking from the top to the bottom, then we’re going to run into another situation like last year.”

And last year for the Mets meant playing meaningless games over the season’s final four months, mostly caused by an anemic lineup and brutal bullpen.

A Mets rotation that lacks any kind of depth took a hit in the fifth, when Vargas was removed for a pinch hitter because of the hamstring discomfort. Tim Peterson, Daniel Zamora and Tyler Bashlor were deployed from a drained bullpen to get the Mets through the afternoon, combining for four shutout innings.

Vargas said he felt a tweak in the hamstring on a strikeout pitch to Travis Shaw ending the fourth and didn’t want to risk it.

“I would say it’s kind of so-so,” Vargas said, referring to the hamstring. “I don’t think I have ever had to deal with any hamstring issues, so I think it’s just more of a let’s see how it is [Monday]. Not panic or rush to any conclusions and we can make an assessment based on how some of the treatment goes.”

With two off days in the next week, the Mets would have the luxury of skipping Vargas in the rotation until May 18 if needed. Of more immediate concern would be finding a potential replacement for Matz, who is scheduled to pitch Wednesday in San Diego.

The Mets (16-18) have scored seven runs over their last five games. Juan Lagares’ solo homer in the seventh Sunday cut the Brewers’ lead to one run, but the Mets never completely closed the gap on a day Jeff McNeil, Robinson Cano, Michael Conforto and Wilson Ramos were absent from the starting lineup to receive rest.

Vargas (1-2) surrendered three earned runs on three hits with five strikeouts over 50 pitches.

Christian Yelich’s mammoth two-run homer in the third — a shot into the top deck in right field that traveled 440 feet — gave the Brewers a 3-0 lead. But Vargas received little help from his defense in the inning.

Keon Broxton misplayed Orlando Arcia’s fly ball to right into a double that gave the Brewers runners on second and third with nobody out to start the inning. Lorenzo Cain’s sacrifice fly gave the Brewers their first run before Yelich unloaded with two outs for his 15th homer this season.

Tomas Nido’s RBI single in the fifth against Zach Davies sliced the Mets’ deficit to 3-1. Broxton doubled to deep center to begin the rally before Nido delivered with his third RBI of the season.

Davies limited the Mets to two earned runs on six hits and one walk over 7 ²/₃ innings. Josh Hader recorded the save with a perfect ninth.

“We got off to a very good start, scoring a lot of runs and not pitching to the best of our capabilities,” Vargas said. “We’ve picked the pitching up a little bit and it seems to have slowed things down a little bit, but I think that’s all just part of the game.”