Hello Dave,
Thankyou for approaching DoctorSpring with your query.
I will need more information to give you an informed opinion.

When you say violently sick, what do you mean? Were you having severe diarrhea and vomiting? Or were you having some other illness?
What other symptoms did you have? Have they cleared now?
Do you have sexual encounters with multiple partners?

If you were having diarrhea, vomiting and fever, you probably had gastroenteritis (inflammation of the stomach and intestine) In some cases gastroenteritis does present with mouth ulcers like the way you described. In such cases the ulcers will subside on their own as your illness clears and is nothing to worry.
You can apply an Over the counter mouth ulcer gel if the pain is troublesome to you.

Please reply as a follow up so that I can give you a better opinion on your condition.

Thankyou