Yellow discharge two days after sex

Hey guys, I’ve been getting yellow discharge literally a lot of discharge two days after I have sex it looks like phlegm. I’ve done a STD and Bacterial Test and I haven’t got neither. I really want to know what’s up it’s been stressing me out.

I went to the sexual health clinic and they told me there’s nothing wrong but I know there’s something wrong. I’ve been to the clinic like 10 times now all day the same thing. The issue keeps happening.

Does anyone know what it is?