Am I wrong for being mad?

I have always helped my sister get things that she needs, like if she asks for money I'll give it to her and if she needs something for my niece I'll pay for it or if she needs a babysitter, I'll babysit for free. Tonight, I asked her could she get me some food because I had woke up from sleeping and I'm really hungry(I still am right now & I'm pregnant) and she says no that she got plans. Like Wtf, I go out my way for you every single time you need it and I barely ask you for shit but when I do, I get turned down. Now she left my niece here while she left to go do whatever the hell she planned for me to babysit. Like wtf??????? Get the fuck outta here! As soon as she wakes up, and cries I'm telling her to come back for her child. I'm just really mad as hell because I always look out for people but they don't look out for me in any type of way. 👎🏼