Hi I Have A Creamish, Sometimes Brownish Discharge That Smells

Hi

I have a creamish, sometimes brownish discharge that smells like rotten eggs. this comes and goes, especially after I had sex, then I will experience it. I have been to clinics, they gave me STI treatments adviced that I should always use condoms, but I used protection but the smell came back. the treatment stopped it, but after I have sex it comes back.