Please help.

It’s Thursday, 4am, and I picked up an occlusal guard “deprogrammer” on Tuesday (I thought this was just a mouth guard, but I might be wrong). I didn’t have headaches or anything like that before using this. They just said that I clench/grind in my sleep and it was wearing down my teeth, so I agreed to pay nearly 400 bucks for this piece of plastic. Well, it’s causing soreness in my cheekbones and I’m hoping this pain will subside? All I was told was that it might be uncomfortable, but I assumed that as people don’t normally sleep with something in their mouth. I didn’t realize soreness was a possibility.

My main question is: IS soreness a possibility? Is this supposed to be happening? Or is it causing more damage as a result? The thing is, I’m upset about the possibility of having to go back to the dentist. These people had me do x rays day one, and I was supposed to do cleaning same day, but they apologized for being overbooked and had me reschedule a second visit to do the cleaning, then I did the impressions day of cleaning and had to come back about 2 or 3 weeks later to pick up the mouthguard. In the process of all this, they overcharged me twice, but took it off (though I doubt they would have said anything if I hadn’t asked them to). I’m a new patient here and want to have 1 dentist that I like and return to for the sake of my dental health, but I haven’t had a great experience yet. Please tell me that this “deprogrammer” situation isn’t their final nail in the coffin, and it IS doing what it’s supposed to?

PS: Will ibuprofen help???