what's going on??? HELP

so two days ago I had sex with my boyfriend, we've always had sex with no condom and everything has been great well recently he tells me his dick is really itchy, like on the bottom near his balls, this started after we had sex. I've been tested for everything it all came negative and same with my boyfriend. does anyone know what this could be?? there's no bumps or anything, just itchy and is there any way to get rid of the itching

there's no redness or bumps or any sort of discharge, just itching