please help me!

ok I'm super stressed and worried right now because I just had sex with my so saturday. We've had sex before now, always protected, and I've given him oral but this time I've had irritation and itchiness down there and when I looked there were some small bumps that aren't open but itch very badly. I thought about it being an STI or STD but if it is then why haven't I gotten it before? and if it's herpes then why isn't it on my mouth? he hasn't cheated and neither have I so what is wrong with me?? I'm terrified that it is an STD that one of us has somehow aquired...