How to stop feeling like such an angry mom 24/7??

Just a warning this will probably be a long post so for those who choose to read the whole thing and give feedback, thank you it’s very much appreciated. To give some details I’m a stay at home wife/mom of a 3 1/2 year old and a 1 year old (both are boys), I work 2 nights a week as a server to get out of the house, other than that we just do the typical outings such as the library, zoo, park, or going to grandma’s. I have a wonderful mother who is always willing to watch my kids if I need the help. At the moment I am in the absolute trenches with my 3 year old son. Before having a 3 year old I thought I had everything figured out down to how we were not going to spank or use any physical punishment’s whatsoever. However, these last few months have been my breaking point, I ended up giving him a spanking which was a very light tapping of the butt because literally nothing else was working. The first time I did it was because he hurt his little brother pretty bad by pushing him down on the ground, I was so angry I made him go to his room and say sorry to his brother but instead of saying sorry he said he wasn’t sorry and that he wanted to do it again while looking me dead in the eyes so I turned him around and spanked his butt. That’s happened a few more times since that day only when he does something to physically harm his brother. I noticed it doesn’t work so I stopped doing it completely and got a time out chair to set in the middle of our kitchen floor with a timer which has been the most effective form of punishment in my opinion. I know deep down he’s “testing” me I can understand that but in the moment it feels like a personal attack. I can’t go to the bathroom, take a shower, lay down in bed, cook dinner, or do literally anything without him being by my side. He has to know what I’m doing at all times, if I’m going to the bathroom I hear him asking my husband “Where’s Mommy I need Mommy!” And my heart rate starts going up to where I feel myself getting angry. My husband is a saint and is very hands on with our kids when he’s not at work. Even with all of the help I have access to why do I still feel so alone and like I have enough anger to throw a car across a street?? It’s making me feel like I’m letting a 3 year old defeat me. I even went to school to specialize in child psychology. I know every single thing I should or shouldn’t be doing with a toddler that will “work” but yet the moment he does something to me it all gets thrown out the window like I’ve never learned a single thing. For example, this morning I was sitting on the couch and my 3 year old really wanted his Alexa to play a certain song in his room while his brother was taking a nap, so I go into his room and try to help him but he just won’t calm down he’s freaking out screaming for me to help him while I’m literally already doing it. So I tell him he needs to be quiet to not wake his brother but he starts getting louder, instead of being a rational mother who tries to hold him and comfort him, I said I was going to throw the Alexa away all together because it’s ruining my life. I’m just worried he’s going to see my irrational behavior and think that’s how he should handle his emotions. I’m worried all the time I try to start the day out super calm but it always ends with me yelling. I don’t know how to be consistent no matter how hard I try. I’m so tired of feeling like I’m doing great one moment, and then feeling like the worst mom for my kids. It adds even more stress that they’re boys I’m so scared they’re going to see my spouts of anger and yelling and think it’s okay to act like that when they grow up because their Mom did it. I’m not abusive by any means, I don’t break or throw things out of anger so why do I feel like I am?? When I get done yelling for the 80th time in one day it feels like I’ve done something so wrong, like I’ve hurt them physically I’m not sure how to explain it really. I’m hoping some other moms can relate to me because I’m very tired of feeling alone. On the bright side it does make having a 1 year old baby feel like a literal breeze! Fingers crossed the torture ends when my son turns 4 and it will all be worth it!🙃