Smelly cum???

I know this a weird question but when me and my SO got together he would cum in me and after a little while my vagina would smell very badly. I went to my OBGYN and got tested for stds stis just in case and yeast/ vaginitis. All came back negative so he started pulling out and my vagine went back to normal. We have been trying to conceive and the smell is back again. I cannot stand it!! Anyone else have had anything similar?

Edit: Thanks for all the advice! Like I said when he doesn't cum in me I have 0 smell! I don't think it's from not washing or being clean but maybe our bodies chemicals don't smell so great together. When he pulls out I smell great and normal. It's legit only when he plants his seed in me lol He also eats ALOT of red meat so I'm not sure if that contributes!