Exact reason for oral ulcers (Aphthous) is still unknown so it has be studied extensively and still going on. Mostly they are related to stress
, allergic reactions, autoimmune responses, and YES, these ulcers can be appeared in mouth due to various other diseases like stomach, intestine ,liver, kidney and blood related. HIV
,syphilis and many more. Behcet's syndrome, chron's disease can cause ulcers in mouth. Dislocated navel will not cause oral ulcers if dislocation is not involving a immunomodulator/immunosupressor/ steroidal therapy. Antibiotics seldom cause ulcers in mouth unless used topically. I hope it will help you. You can do tact me regarding any further queries.