I had yellow discharge for most of the beginning of my pregnancy...it was even "amber" colored at times...the doctor said it was normal..
I had a yellowish discharge without odor around wk 5 and 6 but it hasnt come back again. If you are strongly concerned I would call your doc.
it's totally normal.....I've had yellowish all along and nothing is wrong with me or my babies and I don't take any yellow meds either....my OB said long as it's yellow or white it's ok as long as it's odorless.
It can be normal if any of your medications are Yellow in color, other wise you should speak to you dr if the discharge is yellow and has odur.