Regarding the canker sores and fever blisters. This happens usually due to malnutrition and is common with undiagnosed Celiacs. Specifically
A diet lacking in vitamin B-12, zinc, folate (folic acid) or iron.
Canker sores may also occur because of certain conditions and diseases, such as:
Celiac disease, a serious intestinal disorder caused by a sensitivity to gluten, a protein found in most grains
Since it is a disease of malabsorption you will find that many if not all symptoms you feel can be directly related to specific vitamin and mineral deficiencies. Often I search on google for "what deficiency causes conditions like ie; ringing in the ears, dry eyes, muscle twitches, canker sores, glossitis, irregular fingernails, rashes, loss of feeling in hands and feet". The list goes on forever. Try this and educate yourself regarding deficiencies, worth its weight in gold toward understanding the impact of malnutrition.
You don't mention if the antibiotics were prescribed as a method to treat the canker sores but I am assuming that is what happened, please feel free to let us know if that is a poor assumption.
Regarding the rice, I personally have never heard of rice causing an issue but you must realize that a lot depends on how the rice was prepared and any possibility of cross contamination.
Now that you have been diagnosed as Celiac it will require that you do a lot of research regarding the Gluten Free diet and some of the downfalls due to cross contamination, preparation and general practice of eating safely.
So glad you found this site because it is littered with Celiacs who care and are more than willing to help you and others. I have been gluten-free for 11 years and never eat in restaurants, just my preference because of the bout I had for most of my life.
It is common for certain antibiotics to cause diarrhea even for non-celiacs but more importantly once you maintain a 100% gluten-free diet and supplement with vitamins and minerals the canker sores should fade away.
It can take weeks to months to start feeling normal again, as for me, in two weeks I felt better stomach wise and months for the neurological issue to wane.
For the record, you did not ask too many questions. The people here care and will help when they can.