PORT ST. LUCIE – There are self-doubts. Two years of being sidelined following Tommy John surgery will do that to even the most strong-willed pitcher.

But there is also relentless determination from Zack Wheeler to earn back his starting spot in the rotation.

The Mets right-handler returned to practice Tuesday with his teammates at voluntary camp with but one goal in his sights.

It’s not in the bullpen.

“I know I belong in the starting rotation, there’s no question about that,’’ Wheeler told The Post as he stood behind the cluster of practice mounds known as the six-pack. “I’m a starter. I want to be a starter.’’

There is zero doubt about that.

Wheeler, 26, is aware that he has to run the pitching gauntlet to get back home to the rotation, which probably means a bullpen stint, but there is no way Wheeler wants to fall into the bullpen trap.

He has seen it happen too many times.

“I feel that guys that go to the bullpen get stuck in the bullpen, and I don’t want to do that,’’ Wheeler said. “Because either you are doing bad and you stay in the bullpen because you can’t be a starter, or you are doing really good and they can’t afford to move you out of the bullpen. So you are going to get stuck there, and that’s why I’m trying to let everybody know that I’m not a bullpen guy, I’m a starter.’’

It’s clear.

And, truth be told, Wheeler (49 major league starts, no relief appearances) doesn’t even know if he can handle the bullpen. Forget about back-to-backs.

“I don’t even know if I could do every other day in the bullpen,’’ Wheeler said. “It was a struggle for me to get every fifth day. That’s because I’ve started my whole life.

“It’s the mindset, it’s physical, it’s what you’ve been doing your whole life.

“I know at some point I will have to go to the bullpen thing just because of the innings,’’ Wheeler said. “I hate innings limits, but I guess that is part of the game these days. You’ve got to do what they say. They’re the boss.’’

Wheeler said he talked to GM Sandy Alderson about the situation this winter, and the conversation “re-assured me.’’

He knows the Mets are looking out for him.

He’s had Tommy John surgery, stitches that didn’t dissolve and PRP injections. He’s had too many false starts, but it’s finally go time.

“It’s been fun watching these guys from a distance,” he said of the Mets’ talented starters, Noah & Co. “It’s going to be fun to see if I still got it against big league guys, that’s the way I look it, but I know I still do.

“I just don’t want to get my hopes up too high.’’

First things first, he has to reestablish himself in his own mind.

This has been the longest of roads back for Wheeler, who admitted: “You start to second-guess yourself when you start having some complications. I was supposed to come back last year a couple different times and that didn’t happen, so you start to second-guess yourself. But at the same time you have that trust and believe in yourself where you can sort of push through that every day.’’

Wheeler has been pushing that boulder up the hill since March 2015. Pushing, pushing, pushing, only to see it roll back down again.

“I know I will really be back when I’m starting again and hitting on all cylinders,’’ Wheeler said.

“I let it loose this offseason, it’s coming out good, I feel good. But the real test will be when I throw off the mound here and put that last little bit on it, because that’s when it was barking last year.’’

There has been much too much pain. Now is the time to begin to gain back his spot in the rotation.