Can someone clarify this, intrusive thoughts do they just pop in your head or do you think them up, if you know what I’m trying to say?

I have been ruminating on why I have been having intrusive thoughts on a specific topic. Anyone know why? Where do they come from? It freaks me out and makes me think that it came from a real memory (I struggle with false memory OCD)

I wanted to ask if it is possible to purposely think of an intrusive thought and then shifting your mind instantly to something else? Is it still an intrusive thought if you have been thinking of it 'purposely' for a second? I dont know how else to explain it, but it felt like I was purposely thinking of it. Anyone else had similar experience what happened during intimate moments like masturbation I feel so ashamed cuz the thoughts are so bad they're either about family members children and stuff like that it feels like I think it I just want to know if I'm not alone I feel like a monster because it feels like I thought these things or like I did think these things and I don't know what to do I feel so ashamed and grossed I need help I just want to know if anyone had a similar experience to shed light on because I don't know I feel so isolated

are they truly intrusive thoughts or am i thinking and creating automatically graphic images that i dont want to think? i think it happens because it's too easy once you're anxious abt it. i dont enjoy it. i just saw a trigger and had a graphic disturbing se&ual image in my head.