Irritated...not sure why

I am normally a nice person but I just had
My baby and I feel so annoyed with my SO's family for some reason ...Always saying that my baby is their baby this / that  etc. his dad always takes my pics and posts them on his FB.. His mom always says to put clothes on her , she's gonna get sick etc. like im not taking care of my child..i dont want to feel this way but its just so annoying. Shes MY baby. I can understand the excitement but can I be a mom? Am I wrong for feeling this way?