One side of vaginal wall is itchy, red, and slightly swollen. Rest of vagina is fine. Possible yeast infection or irritation from sex, etc? No std's

Doubt yeast. Herpes? Yeast could do this, but unlikely. Irritation from sex also might be possible. However, I would be most concerned about genital herpes. See a doctor ASAP, the sooner the better for accurate diagnosis (before the irritation and swelling start to improve); or immediately (within 1-2 days) if the problem recurs. Good luck!