How can I get through this?

I’ve posted on here about this before but I just need to vent. I’m 22, my husband is 23. We have two daughters, a 5 year old and a 5 month old. My 5 month old doesn’t sleep, i’ve paid for all the classes and Ive read all the books and nothing works. I probably get about 3-4 hours of sleep a night if i’m lucky and she refuses to nap in the day most of the time. My husband works from 6am-7:30pm everyday. I am beyond exhausted. I have no help and i’m seriously running on empty. My body got absolutely destroyed this past pregnancy. My midwife even gasped when she saw my stomach and arms telling me I have more stretch marks than anyone she’s ever seen. I cry over my body multiple times a day. My sister does esthetics and told me they have a procedure that can really help stretch marks and she’s seen it work wonders before and because she’s my sister she can do it for me for half off. Still in total the cost would be about 3,000, but they do payment plans. I’ve begged my husband for this and he says no which i understand because we don’t have a lot of money and need to save to buy a house. I just genuinely don’t know how to make it through the days anymore, I feel like a waste of space. I don’t think I have postpartum depression, I think i’m just truly so sad by my circumstances and really tired. If anyone has been there before, I could use all the advice or positive words. Thank you.