yeast infection? help

Yesterday I used a new soap and also took a antibiotic because I thought I had a uti (not sure which caused this rash/itch). Didn't have uti ....
Now since yesterday night I have redness, swollen , itchy on inside of vagina lips that are close to vaginal hole. I see some white stuff but can't tell if it's normal discharge or not. I'm thinking to buy a yeast infection cream at CVS or something tonight.
....Any suggestions which to buy and is it ok to use if I'm not sure if it's yeast infection ?(don't want to make things worse) thanks