I think you could easily have early Crohn's. Negative biopsies don't always mean a lot, particularly when you've been on a freaking course of steroids for 3 months.
Even if you can't get a diagnosis of Crohn's right now, try to remove the fob-off IBS diagnosis from your files. It's hard to get a doctor to take your GI symptoms seriously once you get burdened with the IBS label.
Dx Crohn's in summer of 2000. (Yay )
Tried and failed: 5-ASAs, azathioprine, 6MP, Remicade, methotrexate, Humira, various diets.
Had surgery Feb '13 - subtotal colectomy with end ileostomy. First thing to put me into remission in 13 years.
Had second surgery 10th July '15 to reverse the stoma and connect the ileum to the rectum. Officially flaring again. The fun never begins.