I'm glad you are doing the breathing exercises. I can feel your stress even in the way you wrote the question.
On thing that you did not mention is if you spoke about this condition with your OB/Gyn. MUCH of the stress you are feeling is an absolutely normal reaction to your situation - the kids, the husband, the sleep deprivation, breast feeding(?), the job... goodness. But it sounds as though you have been in stressful situations in the past without experiencing the meltdown that you feel right now. In other words, you seem surprised that you are feeling so overwhelmed and defeated. At least, that's what I read into the brief description you offered.
This brings me back to my point: I wonder if some of the stress is being fueled by the seismic shifts in hormones your body is going through. If you add breastfeeding and sleeplessness to the equation, you get the current state of affairs. Postpartum depression can take different forms, and you may have a touch of this. Your OB/Gyn may be able to help assess this and offer an appropriate treatment regiment.
But back to the day-to-day... I would ONLY use the Diazepam as needed, as this will drag you out and make you feel more guilt over being tired (although honestly, it will alleviate the stress for a few hours). My first order of business if you were my client would be to talk to hubby about striking a balance with him. If he is needed to be away as much as he is, perhaps have a nanny help you out. You simply cannot do it all alone - at the VERY LEAST until your little one begins to sleep through the night and you can feel "caught up." The nanny can be hubby at times, or perhaps one of your mothers or even an actual employee, but you need some help or you are going to freak out.
So in order, (a) have hormonal issues checked by an expert, (b) address your concerns with husband and take steps to give you support, (c) continue breathing and controlling your sympathetic response to the stress (d) diazepam as needed only.
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