I agree with pps, Kate3. My DS has just turned 20 months, and he can be a PITA at times. 90% of the time, he's ok, but there have been a couple of occasions where I have bawled at him for whatever reason, and immediately felt bloody awful. It doesn't make you a bad mum, it makes you human. If you are really feeling like you might scream at him again, pop him somewhere he can't hurt himself and go into the kitcahn and make yourself a drink.
Anothre thing I have found that works is toy rotation. DS only has 10 toys a day to play with, but I change them every morning. This stops him getting so bored, and he thinks he has new things everyday. I never used to bother with this and he just had loads of things around him which he didn;t bother with because they were just there IYSWIM. It also means there's less tidying up for me at the end of the day, and we are getting our moneys worth out of all his toys!!!!!!!
On top of that, I have a bag of his fave toys, which come out once a day when I am finding myself drooping. It just has his colloection of Thomas the Tank engine trains and a couple of cars. They will usually keep him occupied for 40 mins to an hour, and it means I can rest a little (I'm 37 wks pg, so I bloody need it!!!!!!!)
Getting out more usually does the trick, even if it's just down to the shops and back. If that's not possible, a pack of crayons and some paper will provide some amusement. DS likes to scribble on the papare, and will then spend 15 mins taking the crayons out of the box and putting them back in again. I find this especially useful when I am trying to prepare his dinner etc, as he will happily sit in his highchair scribbling for a few mins.
Most importantly, do you get any time out at all? I live for weekends, where I can lie in the bath without a little person shouting at me ten to the dozen, or when I can go out to meet friends. If I didn;t have this time to myself, I'd be at the end of my teher. It has only been recently where I realsied that I needed time away, and it has been such a help.
Don;t worry about chatting to your HV. I had a chat with mine, and she gave me lots of useful advice with how to cope when DS is on one. I'd suggest talking to her might be a good idea, (providing you get on with her!)
If all else fails, don't be afraid of bunging a DVD or CBeebies on. Big Cook Little Cook has been known to save my sanity on more than one occasion!!!