My employer only allows I restroom break for and 8.5 hr day.

My employer only allows us one bathroom break per 8.5 hr day & it can only be 3 minutes long. Not only do they time me but, they will actually send a supervisor into the bathroom & she will act like she's going just to make sure I'm in fact GOING. If I need to relieve myself a second time during the course of the day, I will automatically lose one of my two 15 minute breaks I'm allowed per day. Getting to the point because of my not being allowed to go to the bathroom when I need to, I wound up developing a horrible UTI last week. It also that went into my kidneys & I was very close to hospitalization over this. I called in to go to the doctor & the same day I called & spoke with HR. I requested & put in for FMLA & explained my situation to HR. If it wasn't for my employer preventing me from relieving myself then I would have never gotten the UTI to begin with. When HR they got back to me, I was told that I was denied FMLA & to have a nice day. I'm furious. Do I have to continue to be treated this way? Thank you