Please Help!

I adopted my cat, Luna, from a shelter about month ago. Up until a week ago, she was very playful, would attack my feet as I walked, cuddle with me in bed, and sort of follow me around like a dog. She acted the same way towards my fiance, Nick. She wasn't afraid of us at all, she didn't act timid, or scared. Like I said, she was very playful and cuddly. She is 5 months old. A few days ago I came home and called for her like I usually do, and normally she comes running to me. This time she didn't. I found her in an upstairs room with poo all over her bum, like she had diarrhea. So I cleaned her up, and confined her to our master bed/bath so I could keep an eye on her. The next day I went to work, and my fiance was home with her. She said they were cuddling on the couch and she peed on him. So once again we cleaned her and confined her to the bed/bath. The next day she sounded super wheezy, like she had some sort of respiratory issue. Now, a few days later her health seems fine. She's using her box, eating, drinking, and no wheezing sound present. But she only comes out from under the bed for me, and she is very timid skiddish, and seems to be afraid of my fiance, and will even growl and hiss at him. She is the polar opposite of how she acted when I got her. Even with me she doesn't play or cuddle or even purr. Please help, I want my Luna back. I'm not sure what to do. 

Whenever there are behavior changes a vet visit is in order. Luna sounds like she is sick. Cats can become reclusive when they do not feel well.

Considering that she has made a complete 180, please have her to the vet as soon as you can.

I agree.  She really needs to see a vet.  You're taking great care of her, but she isn't well and may need medication.