I can't do it anymore. Please help.

I apologize for the dramatic title, or the unorthodox nature of this post.I just got done crying in the bathroom of my dorm. My body feels extremely shaky and the anxiety doesn't want to seem to go away.I've been struggling with pure-o OCD for a number of years now. I get one of the versions of it, HOCD (usually referred to as "harm" OCD, but can also be an acronym for what I believe I'm going through -- "homosexual" OCD).To try and explain it as best I can, I'll say that it's a "fear" of not knowing your own sexuality, or changing your sexuality almost instantly. Let me give some brief backstory:I'm currently 18 (almost 19) and I have never thought myself to be gay, or even bisexual. All of my crushes growing up were towards females, I only lusted towards females, and I've never had a "gay" thought towards males (sorry if that is a more derogatory term, not my intention).Why am I so scared, now? My mind is telling me, and it feels as if, I've switched sexuality seemingly overnight. This started about a week ago. Gone are the days I've only thought about women, but now I only think about men, etc.I just need some help.. I'm going to contact the psychologist I had back in high school that I used to see for this issue to get some assistance there, but can you guys answer some questions for me?1) Is it possible to change sexuality seemingly overnight? Could I have possibly been lying to myself for 18 years, only to suddenly realize my attraction for men?2) Is all of this panic I'm feeling a byproduct of the anxiety that comes with an OCD episode?3) As you grow up, do you just kinda "know" that you're gay? As in, you know you're attracted to the same sex, and that's just the way it goes?Thank you all, and I'm sorry if anything I said in this post seems rushed, rude, or anything else. I'm in a very bad place right now.