TMI- yellow discharge

So I'm about 4 weeks pp and this was on my pad today, it's yellow substance that smells stinky, like poo. It's not creamy or thick or mucus-like it's just there.

Down there stings a little bit, and I literally just finished antibiotics for a kidney infection. Even taking a poo is hurting a lot and I'm not doing that so often anymore so the only time I feel the need to poo is when I have so much I can't hold it anymore.

Then there's the pounding headaches and the occasional stomach cramps..

Do I have an infection? Do I need to go to the ER?