strange discharge for months!!!

Sorry for the visual! But I gave birth to my son 5 months ago and ever since I've been spotting everyday with strange discharge! I have extreme pain in my lower back and I'm always tired! It feels like I'm getting hit with a train every night. I was checked for stds and everything came up negative!!! They don't know what it is because nothing is showing up on the tests! I went to the hospital and for some strange reason it had stopped the moment she was checking me so she said she can't treat me for something she can't see. She did ultrasounds and found nothing!!! Please! Can anyone help me! They said they have to check me do cervical cancer next!