Itchy right after sex?

My partner and I had sex last week Thursdsy and everything was fine, exactly a week later we have sex again (both without a condom but I'm on the pill) and right after my vagina was itchy. It's itchy right around the bottom of the opening on both sides. Any ideas as to why? It's not unbearably itchy, but I can definitely tell its itchy if that makes sense. It's not inflamed or red either. This has never happened before. It is now Friday (day after) and I am still itchy, any insight would be much appreciated! Update: we've had sex without a condom plenty of times. We've been dating for a year and I've been on birth control for 3 years