Why is it that so many times something that gives me joy, also ends up becoming an OCD trigger? Does this happen to anyone else?

Absolutely. I have harm OCD and when it acts up intensely, I have to ask my parents to take care of my dogs. My dogs are my world and they make me so happy but when my intrusive thoughts come up, I sometimes feel like I need to make sure they're safe (which is just feeding the OCD so I now know I should just sit with it and not have my dogs stay with my parents).