i have anxiety about going to the bathroom.

I have like this paranoia about everytime i get gas or cramps or someone else in the house has the runs or cramps or gas or stomach aches or any problems with their stomach that i will suddenly magically come down with a case of very irritating bowel movements, i know it's gross but every time i feel like i need to go to the bathroom i feel like it's eventually going to turn into diarhea, and i get horrible cramps.. it doesnt happen all the time but when it does it's very annoying.
when i was younger for some reason i would hold my bowel movements, i know thats not healthy at all but for some reason i was really afraid and i would hold it until it was hard to get out and the stool was huge, i did that for a long time.  it's gotten better now so i have no problems with my actual bowels. i just have paranoia and phobic ideas about stomach aches and bowel movements. i'm afraid to go to the bathroom sometimes because i think it will end up being a bad poo.
i know this is really gross and all, but i have nobody else to share this with and i know i'm not the only one in the world whos afraid of this stuff, i need to find out WHAT memory is triggering this fear.