So I have begun referring to myself as a lesbian when talking to people. This is not a huge step as these are people who already knew I wasn't straight and/or people I only know on the internet. (Which is not to say I don't value the friendships I have on the internet.) But I keep having all these doubts. "You can't be a lesbian! You're 50 and you've never even been with a woman!" or "You still have fantasies about your male celebrity crushes!" or "You just don't like the idea of being bisexual so you convinced yourself you're a lesbian!" or ... tons of other reasons I "can't" be a lesbian. Is it normal to come out but worry that you're lying? Part of this could be "denial" but I'm at a loss at to why I have so much denial after coming from a family that wasn't very homophobic and being a big "ally" in college. I did spend some time in a repressive religious environment so I suppose that doesn't help but in my life before that I was not like that at all... yet at that time I felt like I couldn't say I wasn't straight and something like that is still happening to me.
I'm only out to my therapist, who I started seeing a few weeks ago. Since then I've experienced some of what you're describing. Just random 'What if I'm not gay?' thoughts, with no real reason behind them. I think it's fairly normal, but someone with more coming out experience will be able to give more insight. Hopefully they'll be along soon.