mother undermining me being a mother.

I have a one year old and I work full time. While I'm working my mom watching my son. 
Every time I come home she tries undermining me. "How much medicine did you give him" "did you try feeding him real food" "he needs to eat real food" etc 
I KNOW HE NEEDS TO EAT RRAL FOOD. I feed him. He isn't a big eater. And the whole medicine thing.. She does that with everything. 
"Did you do this, did you do that" and I always answer her and say well yeah I know he needs to eat real food, blah blah (sorry if I'm not making any sense) 
She also tells me I don't need to "yell" at him when he throws fits. And yes he throws fits. Hits me and stomps his feet. All I really say to him is "NO THAT IS NOT OKAY" and usually put him in his crib for kind of a time out. 
My thing is - why the fuck does my mom keep questioning my mothering skills? I think I'm doing perfectly fine.