Canker sores remains a mystery, cause unknown, and sores in the mouth of various kinds, both aphthous stomatitis and other problems, occur with increased frequency
in AIDS -- but like
yeast infection, this also is a sign of full-blown AIDS, not early HIV infection.
Finally, I hope you asked your partners their HIV status. Among men who have sex with men, "do ask, do tell" is just as important a part of safe sex as using condoms for anal sex.