OK, found it. It is Jerry Sohl's The Time Dissolver and you can find it e.g. in The Seventh Science Fiction Megapack.
UPDATE: that said, the same beginning ("a man wakes up with amnesia next to a woman he doesn't recognize, who turns out to be his wife") is used in "When the Past Went Away" by Robert Silverberg, a short story where a madman poisons the water supply with an amnesia-inducing drug. The effects of this drug partly wear out in time, so that the people involved live again their lives in flash-forward. In Jerry Sohl's novel, instead, only the mind device can bring back a memory it suppressed.
Hero wakes up in a bed next to a sleeping woman he doesn't recognize.
...his breathing not that of a sleeping man as he looked away from the shining black hair and neck and shoulders and saw that the room was strange to him. He looked back at the girl as she stirred again, turning to him, a movement of arm dislodging the covers to expose a well-rounded shoulder and breast, eyes still closed in sleep, her full lips petulant, as if she were waiting to be kissed. She was pretty and he let it go at that, forcing his eyes back to the room itself, the pebbly white ceiling, gray walls, blinded windows, desk, drawer, bureau. Sherwood slipped quietly from the bed, stood looking down at the sleeping girl, decided she was in her late twenties, then with a shock discovered he was naked, which was not as much of a shock as the discovery that his pajamas were in a heap at his feet — not his pajamas, but a man’s pajamas. He was tempted to put them on, then saw a man’s clothes on a nearby chair: blue shorts, white undershirt, gray herringbone trousers, white shirt, maroon tie, suitcoat to match the pants, maroon socks and black shoes. He had no recollection of owning these particular clothes...
He thinks he's a teenager but discovers himself in an 'older' body
It was then he saw himself in the garage window and jerked back in surprise. Can that be me? He forced himself to stand quietly while he inspected his image. The man who stared [...] distortion. Where was the change? He moved closer, studied his reflection carefully.
And suddenly he knew.
He was older.
Turns out he is a scientist who invented a technique to cause memory loss and was using it to 'revert' short bursts of time - 20 minutes or so at a time
“There were some side effects,” Ollie was saying. “You found using the memory suppressor made it easier for you to solve problems. I guess it gave your mind a rest; at least that’s what you used to say. At night you’d set it to erase a week or so and the next morning your mind would be able to cope with the problem you were trying to solve a lot better. Rested the mind, sharpened the memory. You said you found yourself remembering things you’d forgotten years ago [...]
But a rival scientist used the device on him to revert back 20 years.
Sherwood smiled. “Not at all. I think I know how he did it.” “How?” Sherwood turned to Ollie. “How long would it take to erase eleven years from a person’s life?” “Oh, five or six hours. We found out you erase about a week with each half minute. The same for coming out of it, too.” Virginia shook her head. “I can’t see Dr. Schlessenger sneaking in, leaving the machine and coming back for it in six hours.” “Of course not,” Sherwood said. “That would be too risky for Schlessenger. He’d never take a chance like that. But I know how he could do it without ever leaving his room.”
“Our rooms joined,” Virginia said. “I see how.” “Of course. He probably visited us, saw where the head of our bed was, right next to the wall separating our rooms, knew at once this was the opportunity he was looking for. He sets up the machine in his place right next to the wall and the outfit works through the wall on us, Schlessenger staying as far away from it as possible.”