I think most of us can say that we've had yellowish discharge. With under panties now being lots of colours, we often don't notice what colour the discharge is but, with lighter colours, it may be more apparent. And, don't forget that a lot of women just don't take any note of things like this. As long as they're not bleeding or feeling uncomfortable, they don't really look or care.
It could be that if you were to ask a number of women to take note of this sort of thing, you'd find that most women have this.
The fact that you have been checked out gynecologically and treated for infection with no change, means that it's "normal" for YOU!
And, as Kszan has said, it may be urine leakage or not a full cleanse while wiping after urinating. (That's one of the reasons why/usages for panty liners being invented) Urine is yellow and can stain yellow.