Hope you saved your receipt it looks like it is well on it's way to croaking.

Maybe it doesn't like where it is planted, could it be too close to the A/C unit? Maybe the heat off of it is too much for it.

:) Aqua

Aqua is absolutely right!
Is it still in a pot? Is it in the ground?
In any case, move it. Put it in part sun to full
shade for right now and watch it.
It needs cooler air and no sun for a few days.

Looks like a whitefly infestation too.
Bright light, not full sun while you find a better
planting spot. Don't fertilize it..it's stressed already.
Put it in an airy spot out of the sun and don't water unless you're certain it needs water.
Once you get it in the ground, don't overwater it.
See what those white specks are and if they really are whitefly.

It needs WATER--SOONER rather than later. AC may also be a factor if the area is hot and breezy!

The white specks look like white fly, and the stems turning black is sooty mold from aphids. And the AC unit will put out too much hot air, and the drooping leaves are a sign of moisture stress.

I would move it to a spot with only morning sun, keep it properly watered, and once it stabilizes, treat it with Bayer systemic treatment for whiteflies.

It's on the back patio in a well draining pot. I re-potted the plant once I got it home from the store. I've just recently moved it next to the air conditioner to get it out of the direct sun. My back patio gets full sun from noon to 6 pm. I'll have to move it close to my patio glass door to get it out of the direct sunlight.

The soil is still damp, and it rained last night, so I won't water it. I'll move it and let you all know how it goes. Thanks!

I've posted a photo of were I moved the plant on my patio. This is the only spot that gets the least amount of sun. There were no white spots on the leaves. I think that was rain drops on the leaves in the previous photos. Shouldn't I be spraying it with something? The leaves are starting to turn brown and fall off.

Another photo that shows how much worse the plant has gotten in one day.

When you repotted it, was the potting mix also fast draining?
What kind of potting mix did you use?
It might be ok after all the drama of the plant.
Gardenias complain alot when they are stressed, and repotting it really stressed it out big time.
Does the pot you put it in have a real big drain hole in the bottom? That isn't really a gardenia pot.
You may be better off planting it in the ground if it lives until September.
Gardenias hate pots. They love it in the ground.

I used Hyponex All Purpose Potting Soil by Scotts. I don't know if it's fast draining. After re-potting, the plant showed no signs of stress and bloomed beautifully. However, after the last bloom, it quickly started showing signs of strees with drooping leaves etc.

Don't know where I could plant it in my yard, were it wouldn't get too much sun. I don't have garden. I might try a larger deeper pot, and a potting soil better formulated for gardenias.

I would change the potting soil as soon as I could, I have used that an it turns into cement. Nothing likes to grow in it.
I just recently dumped a bag of it I had purchased a long time ago when I didn't know any better, it was a solid mass of junk.

The plant would be happier in the ground, none I have ever tried in pots made it. My mom has a plant and I got rooted pieces from her in the past. I have gotten a few an wasn't ready to plant them when I got them, the ones I got in the fall didn't make it threw the winter the other ones I got in the spring and didn't make it through the summer.
If I get any more from her, I will have a place ready to plant them and I will get them in the fall.

Good luck with this one, I really hope it perks up.

:) Aqua