If you think about a intrusive thought on purpose is that rumination?

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

Please how can an intrusive thought be distinguished from our own thoughts ?