I'm get so annoyed when I ask my mom to watch my son for me to go to work and she says no. like…

I'm get so annoyed when I ask my mom to watch my son for me to go to work and she says no. like forreal. I'm a single mom, I work full time, and I'm 8 months pregnant. I have a baby sitter usually, but she specifically told me she can't watch my son this Monday and Tuesday because her work will be keeping her late. I give my parents so much money every month to keep them going because they are so financially irresponsible and I don't have anyone else to turn to. My ex husband refuses to keep our son any extra days other than his weekend visitation. Its just like wtf. I'm constantly helping you out when you need it, but I'm in a bind and you're willing to let me lose my job because you don't want to take my son with you to go to a "cheer celebration" for my niece. Nice to know who takes precedent.