Gums are swollen, multiple canker sores developed, teeth are in pain and unable to eat. What is it? And what might have caused it?

Possibilities. There are lots of possibilities, 2 many to name and describe. Although relatively rare in US nowadays, ANUG (Google it) is 1 possibility: more common years ago with patients your age under extreme stress, little sleep, poor diet & very poor oral hygiene- bacteria grow out of control and toxins cause severe pain\ulceration to gums. Again, could be other things. See a dentist for diagnosis\treatment.
See a dentist ASAP. (ANUG) Acute Necrotizing Ulcerative Gingivitis is a serious infection of the gums that causes swelling, ulcers which later form necrotic (dead) tissue in the mouth. Keep proper oral hygiene, nutritious food, overcome stress and see your dentist 2X per year and you will be far from this disease. Now call a dentist for an emergency appointment. Good luck.