Help me please

okay hello ladies, so I am having a little bit of trouble with my two-year-old son, I am a fair mother and I try not to yell at my kids, I also have a eight-year-old daughter and I just got done yelling at her because she tends to not listen to me and always ask me why after I tell her to do something and give me attitude, and after I got done yelling at her I just felt really awful to the point where I started to cry and I guess I end up letting her have her way every time and I’m just trying to break the cycle that I have for my kids to act and treat me any kind of way, now my son who is about to be two he literally has to be up under me all the time and I am a single mother and literally exhausted from working all day and I have tried everything from letting him just cry but he will literally cry for hours and even sometimes throw his self on the floor and he hits his head and starts crying even more and it makes me feel bad so I let him lay with me but I just want them both to break out of the cycle, my daughter for her not listening and somewhat disrespectful and my son for always wanting to be underneath me and thinking that it’s the end of the world is I’m not always paying attention to him, can one of y’all please help me???