Anna, you are treating the Gardenia like it is a frog. It is not happy here, you move it. It is not happy there, you move it. It isn't happy there so , you move it again. That is not a good idea. It can't get use to any one spot.
They do not like intense heat.
They like good morning sun, then shaded for the rest of the day.
They like to grow moist in a well draining soil. They enjoy soil on the acidic side, around 5.8 to 6.4.
And stop fertilizing it so much. Fertilizer is meant to support good growth. It does not create it. You really can't cure bad culture with fertilizer. Fertilizer is not medicine.
Indoors they might be happier being generally cooler but indoor window glass cuts down on light intensity. You would need a sunny spot inside with 6-8 hours of sun. Put it right in the window, not off to the side or across the room.
If growing outdoors, nice sun in the morning, shady in the afternoon. Never let it go dry.
