Why does this happen

Why when I'm over my anxiety & calming down trying to enjoy life my mind go crazy & fill with what if thoughts like the little thing set me off & I hate it like I start randomly crying and thinking the worst in life like I could have sex with protection and think the worst like maybe i have blah blah or i think people don't understand me I wish I had someone to vent to or someone to understand when my mind goes wild I wish I could feel happy without thinking the worst and I wish people can stop telling me to calm down and i hate that I feel bad for myself...