I feel like I’m failing as a mom

I have a 14 month old and a 6 week old. My husband has already gone back to work and he is going to school full-time so I’m basically living the single mom life. The hardest time of the day is in the evening when it’s getting near my oldest baby bedtime. It seems to never fails that when it’s dinner time to feed my oldest the six week old start crying... he hates being put in a baby chair and just cries the entire time that I feed the oldest. The oldest of course throws all his food in the floor and acts a fool at the table most of the time and I literally have to walk away from table for second because I have too scream in my own mouth and not let them hear me but I am about to lose it. Then it becomes around bedtime but in-between dinner and bedtime one of them screaming and crying or both and never fails my youngest wants to be fed when I have to put my oldest to bed. So I get the oldest to bed later so I can feed the youngest and then again have to sit the youngest in the chair and he screams the entire time my oldest screams and it takes all I can to keep my patience because I feel like I am losing it hearing all this crying for the last for five hours and other parts of the day and I catch myself sometimes just snapping at them and I feel like a horrible mom. I try so hard not to snap and yell but it has happened once or twice and I immediately feel like a piece of shit and I sometimes feel like they would be better off without me. Yes I am on medication for postpartum but I feel like sometimes it’s more than postpartum it’s the adjustment of going from one from 1 to 2 children and the lack of sleep from the newborn that makes a recipe for me to be irritable and short. I guess I want to know from those with more than one child that are close in age does it get better? This is just a small snippet of my days alone and I feel like I am losing my sanity.