Your fingers don't have muscles so your teacher should be teaching you how to use your arm to play. If a teacher tells you to "release tension" ask him/her what you should replace it with. Something needs to depress the keys if not the fingers, what could it be . . . ?
Don't press into the key bed. Once you depress a key using the weight of the arm, leave just enough weight to "rest up" while leaving the keys down. Pressing down strains the long flexor tendons in your forearm.
Ask your teacher about the height of your bench. If you sit too low or too high you will create tension in the wrist, neck, shoulders or back.
Again, the arm places the fingers and if there is no arm movement you may twist the wrist. This is called ulnar or radial deviation and can cause problems with both playing and fatigue.
Ask your teacher the importance of in/out and up/down. Also ask how the pronator and supinator is used in playing. If they don't know or don't have an anatomical answer. . . find another teacher.
It is my and only my opinion that 90% of teachers should not be teaching. Just because they took lessons doesn't qualify them to teach others. They only know what they know and not what they don't. You wouldn't go to a doctor who doesn't know anatomy. You wouldn't bring your car to a mechanic who doesn't know how combustion engines work. You wouldn't take ballet from a teacher with only cheer leading experience. You wouldn't vote for a reality star to be president. You wouldn't take flying lessons from someone who only plays video games. All these people may be good at what they do but a piano teacher needs to know anatomy, physics and ergonomics. Not just music.
Here is a question for you: If every time you bend over to pick up a box, you throw your back out. Which teacher has the best answer:
A: You need to do exercises for strength and endurance
B: Take a break, you're lifting too much
C: You need to lift more
D: Lift from the knees
So if you have fatigue and pain from practicing the piano:
A: You need to do exercises for strength and endurance
B: Take a break, you're practicing too much
C: You need to run scales and finger exercises
D: Play from the arm