Hi Margo
I remember your other threads, I have a ds same age as yours. It is great to hear that your ds has been assessed as normal and bright. I am also very pleased that you are going to start on CBT. I know you have been very anxious about your ds and his health / development, and that you have had some very good advice on mumsnet about looking into why you feel this way, rather than focussing on ds.
As to the plug obsession - my ds loves putting the plug (ordinary one not pop up) in the sink and filling it with water, pulling the plug out, putting it back, turning the (cold only!) tap on and off. I think it is a very normal thing for children, particularly boys, to be interested in how things work, and they will concentrate on some things, or go back and back to the same thing for weeks on end!
I am sorry it all went so wrong for you yesterday. I have been in the same position as you of shouting and then feeling terrible. You have learnt how to manage a situation like this and your son will have forgiven you don't worry - at this age while being shouted at is not nice, as long as everything is now better and he feels safe with you (which I think your time with him on the bed demonstrates) then there is no harm done.
FWIW your standards of cleanliness are way above mine!! A few germs will not harm your ds, in fact they will help to build resistance, if he only ever plays with sterlised objects or on surfaces cleaned and wiped every hour he won't be building up any resistance for the future. Don't be afraid of letting him get dirty. I wouldn't let him play with the toilet brush (!), but I think a plug which has had a clean recently and isn't obviously gungey or horrible isn't going to harm him, particularly if he's not putting it in his mouth.
HTH. Am thinking of you and wish you all the best for Thursday and onwards.
(I posted on some of your other threads but have changed names since and can't even remember what name I used on that one. Can't seem to find a name I like).