Had something similar with periods, but didn't notice my breasts shrinking (pity :-/)
I never related the prolonged periods to Entocort, but now that you mention it, I think it's possible that the two could have been related. At any rate, since coming off the Entocort my periods seem to have gone back to normal and aren't being dragged out over 2 weeks any more.
That said, I can't remember pred affecting my periods in any way and it is a stronger steroid than Entocort. So I dunno. I can't really help you I'm afraid, but let us know what your doctor says.
Dx Crohn's in June 2000. (Yay )
Tried: 5-ASAs, azathioprine, 6MP, Remicade, methotrexate, Humira, diets.
1st surgery 20/2/13 - subtotal colectomy with end ileostomy.
2nd surgery 10/7/15 - ileorectal anastomosis. Stoma reversed and ileum connected to the rectum.
Current status: Chronic flare. Do I have any other kind?
Current meds: 50mg 6MP