Brownish yellow discharge and smell?

I’m 4 weeks pp after a csection and my bleeding has for the most part stopped just here and there. But today I noticed some lochia that was brownish yellow in color and it has a horrible smell like not to be tmi but sour? Can this be normal or could this be infection. Will be calling my OB but they are closed for the weekend and I just wanted to know if this is something I should take more seriously and head to the ER. Not having any other symptoms other than cramping on and off