I got kicked by a horse in my lower back and bottom on Wednesday. I have severe bruising. Have had an xray and no fracture was seen, pain is 10x worse

Trauma. Unfortunately, plain film x-rays are best for diagnosing fractures of bones, and are not very good for finding injuries of the soft tissues, such as ligaments, tendons, muscles, etc. Although you may have not sustained any bone fractures, soft tissue injuries can be quite painful. If your pain is not getting better, or is getting worse, seek medical attention.
Go Kick It Back !! A horse kick ain't no bucket a jelly! If you are still hurting like that in 10-14 days, that may warrant another x-ray or two to see if there might have been a latent fracture. And anyways, there's a lot of other stuff in that area that can hurt a lot, even just a bone bruise.I had an injury in that area once and it hurt like Hell. It should*start*to feel better in about a week or 10 days from now.
May need an MRI. May have a herniated disc or epidural hematoma of the Spinal Cord. These not seen on plain x-ray.