After having sex, i found part of my vagina was red, any ideas?

i had sex last night, we used a condom, but i found it hard getting comfortable when trying to sleep, i just fault maybe it was because i hadn't had sex in a while, today i realized the left side of my vagina was red, i don't find it sore or have any pains, i was just wondering if anyone had any ideas on what could be causing this?