Spit up with breastfed baby

My baby turned one month and suddenly started spitting up a lot. She hardly ever spit up before that. I was having issues producing enough milk but she’s steadily gaining weight now so I’m guessing my supply must be good now. Does the spit up mean that she’s over eating or is it normal? Should I feed her again after spitting up if she’s fussy? I always burp her after a feeding