Stinkypants (you need to change that name!) seriously it is obvious that you are struggling to keep "all the balls" in the air at the moment and that you are really stressed out. I think when you are feeling like this, it is very difficult not to get majorly irritated with small children. I have depression and anxiety but kids all flown the nest a long time ago. I can get irritated with the cats! You have so much on your plate and I feel so sorry for so many of you young mums on these threads.
When yu say you "lost" a close friend, do you mean she died, or the relationship died, though in a way it doesn't matter which way round, because you are still grieving and feeling guilty, and the combination of those two things are enough, without everything else, kids, house, work etc ect. Bereavement is the same whethere it's a death or a loss of some other kind, and I think you need to be able to bring your feelings outinto the open which would mean finding a god therapist who is experienced in bereavement counselling.
I wonder too if you have been a bit hyper-sensitive just lately as you talk of semi-falling out with friends, and maybe pushed them away emotionally, and you are acting the part of not caring anyway. I think if you were able to show your vulnerability to your friends they would understand and maybe be more support to you.
Re the biggest issue - the catastrophising things and constant worrying about awful things happening. I am no medic and don't like internet diagnosis, but I wonder if this is some kind of OCD. I think many people (me included) worry about our loved ones, and fantasise that the worst has happened, and even "planned" the funeral. My kids are all in their 30s but if I can't get them on the phone I start worrying, and sometimes if my DP is on the phone I imagine it is bad news about one of my sons, dils or gr/chdrn. If I am in bed and can hear him sounding a bit worried I am lying in bed tensely waiting to hear the worst. I think this is anxiety that was passed on to me as a child by my mom as she was quite an anxious person. However, I think with you, this might have got a bit out of control and then you need some help.
I agree with the other poster - can you find an empathetic GP in your practice (there are usually a few - mainly women!) and talk to her about how you are feeling. There are possibilities of mental health issues, maybe depression, anxiety or something similar. You may need meds or you can be referred to a CBT therapist by your GP which might be helpful in helping you to break down this cycle of worrying.
I don't think this is "ordinary" stress (whatever ordinary means) and neither do I think it is wildly abnormal. I think you need some help to get you through a very rough patch in your life.