Nipples don't change for no reason, athough psychmeds can affect them. Everything else can be explained away, but your aeriolas seem like the give away.

Hope I'm wrong because you don't sound like you want to be pregnant, although that's hard to believe from this angle because you don't use protection, and know where babies come from, so maybe on some level you do want a baby afterall.

Buy a test at a pharmacy and in future if you're going to partake in mature activities, be mature about it and practice actual safe-sex and not this Russian Roulette BS pullout method.

Best of luck to you for whatever the future holds