It's very possible that you do have a yeast infection. Herpes won't show up that quick.
Totally agree with Tickiemctickface. Herpes symptoms take at least 2 days to show up. If your partner had a yeast infection, it's possible you got that.
If you are having sex with casual partners, and aren't using condoms, any one of them could transmit an STD. Yes, obviously the more partners one has the higher the likelihood of having an STD, but please don't fool yourself into thinking that those who have only had a couple of partners aren't a risk. It only takes one time.
I'm not sure why herpes is scaring you more than anything else, but unprotected sex means that you are at risk for all other STDs - gonorrhea, chlamydia, syphilis, NGU, HPV, and HIV.
You can test for gonorrhea, chlamydia and NGU at about 5 days post exposure.
You can test for syphilis at 6 weeks post exposure, though it can take up to 3 months, so if you have any unusual symptoms, you might want to test again at 3 months.
You can take a 4th generation HIV test at 28 days.
If you test for herpes, do a type specific IgG blood test. Most will test positive by 6 weeks, but it can take up to 4 months.
If you've ever had unprotected sex before, test for everything now, and again at the appropriate times for this exposure if they are negative now.
I don't mean to scare you more than you are now, but people get fixed on one thing, and forget there are other things they need to test for.