OP, you have my complete sympathy - you are working flat out and, at this point, not getting any pleasure or satisfaction from your efforts. It is no wonder you are miserable and exhausted. The fault is not in you at all - you are obviously trying very hard. The problem lies in the circumstances of your life at the moment - full-time job, three very young, lively children who require a great deal of attention, and very little support or help.
The trouble is that as soon as one shift ends (your full-time job), another starts in the form of looking after your three boys. You have not specifically stated it but I gather that they are noisy, demanding and competitive a lot of the time, which is completely natural at their age and given the fact that there are three of them. Little boys often act "as a pack" when together and can egg each other on to be silly and can be very hard to control, let alone enjoy. If you are being left with them most of the time, you must feel you never get a moment of relaxation or "me time". It's no wonder you sometimes feel like walking out on the whole chaotic situation!
I think, to save your sanity, you have to drastically rethink, and restructure, your weekends as, unlike when you are at your full-time job, this is time which is (technically!) under your control. The reason a lot of parents - both stay-at-home and working - find weekends stressful is that they are unstructured and therefore have the potential to become both boring and chaotic. Children of this age unfortunately need organization or they rapidly make their own entertainment in the form of fighting or unruliness!
The first step is to get your husband on board and persuade him that charity begins at home! The boys and running of the household are fifty per cent his responsibility. Either he takes the boys out while you sort out the household chores in a quiet house or you both take them out for a change of scene and look after them together. I think it is vital to put quality time with your children before anything else at the weekend - as well as this being good for them (and what childhood is all about), it makes things easier for you as hopefully you will have tired but happier children to deal with in the evening. For three boys, I would take them all out for most of the day to a National Trust property or similar where is plenty to do for several hours - gardens to run in and play hide and seek, a play park with swings etc. Take a picnic, let the boys help to choose the food (and treats) and make eating lunch part of the fun. Or, take them all to the tearoom and have a snack there. Vary the place you go from week go week but try to have a day, or most of a day out each weekend. The boys will love it (despite the fights!) and you will have a change of scene and some fresh air. Nearer to home, on the other weekend day, get your husband to take the boys out to play football in the park, to the cinema, or bowling.
Plan the weekend, make it enjoyable (and energetic for the boys!) and you may find things improve a lot. You are in the middle of the most demanding and tiring part of your boys' childhood - things will get better, OP! Don't lose faith in yourself - you are doing a great job even though you don't realise it.