What Causes Swollen Sternum When Suffering From Diverticulitis?

I have a swollen sternum, when I eat I get bloated due to Diverticulitis. I thought I was having a flare-up and went to a urgent care. They prescribed me 2 antibiotics ( Ciprofloxacin and metroNIdazole.) Took both for 4 days, then went to doctors she discontinued the metroNIdazole. That was on Wednesday, now I have been bloated for about 2 weeks and my sternum is swollen. Having hard time breathing and in a lot of pain. I have been having black stools for 5 days now. Every time I have a bowel movement it is black. Is this serious?