Oh gosh, I really feel for you all. When someone is in a flare up of anxiety the whole household can be held to ransom by it. It is awful sustained stress. I am really confident that the worst will pass though, it may be an ongoing issue on and off, but even without treatment these things go through phases.
Thinking about how young he is, I would be tempted to keep it really simple. I had a very bad spell when I was about nine and I found it helpful to have little changes. For example, I got two goldfish to keep in my room which somehow felt like company. I have also found that anything that is a big distraction or change of scene helps. If he was older and this problem was of longer standing it might be different, but at this point whatever moves him on is good, without worrying about whether all the causes and treatment paths have been explored.
I completely understand why you lost your temper, any human would in this situation. It doesn't help the sufferer but it is inevitable.
It is probably tempting to reassure him a lot. That has a place initially especially I think when parents can be very good reassures to young children, but doing it repeatedly about the same things keeps the cycle going. it can also validate the idea that his fearful thoughts are important and require some kind of response, when actually he needs to accept that while the fear may be there, it is not a logical fear and he doesn't have to do or think anything in response. That pressure to allay the fear or do something to protect himself actually keeps it present, flags it as a real threat when it is really just anxiety. If you 'stay with' the anxiety and accept it without acting it will eventually fade.
That is really hard to grasp and harder to do. I would talk to him about his fears to factually correct him and reassure him, but then he has to learn to live with doubt. At first it is awful, but it will lessen once he stops fighting it so hard. He is probably trying so hard to get the anxiety out of his head and the more he does, the worse it gets. Suggesting that it is ok to feel scared or worried but that it will pass, maybe in the sense of a 'worry monster' who says silly things, but isn't right. So he can say 'that thought is just the worry monster, it isn't real, I might keep having it for a while but that doesn't mean it is true or I need to do anything'.
Non specific reassurance though, like cuddles etc, and anything he enjoys that might raise his mood, are good.
Also pointing out that even if, God forbid, a spider intruded and he was scared, in a few minutes it would be over and that he would cope. Encourage the belief that if bad things happen he could cope and survive.
Try to limit, and I know it is hard, the extent to which he feels his problems are causing trouble for everyone. Scans show that guilt lights up the same areas of the brain as the ocd/anxiety and makes it worse. There is only so much you can do but still.
Sorry, I feel like I have explained that badly but at great length! Please ask me anything if I can help. Rest assured that his anger is just frustration and the stress of being in constant fear. I also have anaemia and joint problems so I can see how hard it all is for you right now.