So long story short I just want advice

I started a new job in January and ever since the company has not gotten my payment correct like it's way off I'm supposed to get 1800 a month but it's split between 2 paychecks and this month first check was 190 2nd check was 260....I'm also the one who noticed that they made a mistake and we're paying my rent and the agreement was I wanted to pay my own rent so in return they company knows they owe me back payments like a lot, I'm ready to quit but I honestly feel super bad because I am expecting my 5th child at the end of July and I haven't even gotten anything for her and other kids have birthdays coming up kids need stuff in general. My issue is if I quit what if they don't give me my back payments they owe me (yes I have every paystub) I'm already behind in some bills I'm just super stressed