What is this?

I'm having awful stomach pain and nausea and it's really worrying me and scaring me

Two things are happening: I get thoughts that just keep looping. They almost feel like song stuck in my head. Also, I’ll imagine something and I feel my stomach drop. Then as the seconds go by I keep getting fragments of the this thought but with different details. For example, it’s kinda like how a “vision” is portrayed. I’ll get a glimpse of the thought and then it’ll rapidly expand into something worse every few seconds. I don’t know if I’m causing this or if it’s just an automatic thing like any other intrusive thought. It feels unavoidable, idk if this is a compulsion or if it’s just another manifestation of an intrusive thought. Apart from that remembering an intrusive thought triggers the full thought again and then it just keeps looping or expanding. I don’t know how to stop any of this. Help?

i’ve been dealing with this “thing” since i was 15. (i’m 23 now) if i have a bad memory that i have done when i was really young or just an intrusive thought i feel like i need to tell my mom or boyfriend. it’s been on and off ever since but since January hit it’s been an everyday thing about the littlest things. mostly about my relationship. an example is i was talking to someone random at my job and we were talking about taxes and when im in deep thought or just thinking i do a thing where i bite my lip (not in the sexual way) and i had a thought when it happened “was that sexual?” and i felt like i did something wrong and i went for a while thinking that until i told my boyfriend about it. or like my ex’s face has popped up in my head in the most inappropriate times and i feel the need that i have to tell him. (my ex was not a good person) i feel like im a prisoner in my head everyday, trying to justify thoughts or remind myself that its just a thought. i didnt know that this was or could be a form of ocd. it runs in my family but i’ve just never considered it being this. i always called it anxiety or depression but i always felt like it is more than that.