I suppose it depends on your HV - I have only ever had one who has been helpful, the rest have been a waste of time.
Sadly, I think most of us have been there with our 4 yo boys - as psycho says, it really is a testosterone thing - and I know how depressing it is - I have cried many times over it with ds1 too - and ds2 is just starting to show signs of going through it, which is even worse as he was always such a loving little chap, whereas ds1 has always had a tendency to do this.
Reading Raising Boys and Toddler Taming really helped me, as it reinforced that is developmental and was nothing I was doing wrong, which I think makes it much worse. I also went to a bday party this week a girl's, with 10 girls who sat sweetly (by comparison) and made stuff and 4 4yo boys who just ripped through the house - I had never met any of the boys' mums before, but it was like talking to a mirror discussing what we were going through.
I went on a parenting course about 4 months ago, and one thing that was suggested that really helped was 'special time' - 15 mins together at the end of the day to do whatever he wanted - only caveat was that it had to be with me/dh not telly. We have made stuff, played games etc. It is never banned, even for dreadful behaviour, just a time to let him lead the play. It really helped, even though I thought it wouldn't.
The other things I did were to keep a diary for a week of the worst behaviour (for us ds1 has 2 siblings and a lot of his aggression was directed at them, but not sure if you are in this situation), and what we had done immediately prior to this. I found out that his diet played a part in this (I'm fairly careful, but the odd thing does creep in) and changed it, which improved things. I also changed my responses to his behaviour - finding ways to really praise him out of the blue for any tiny thing he did well - be it come to me fairly quickly if I asked, or put his washing in the clothes bin - which helped me to focus on his good stuff too - it had an effect way out of proportion to the behaviour.
Sorry this post is so long - but you are NOT a bad mother - boys are HARD at this age. I keep telling myself that this stubbornness of ds1 will mature into qualities which will help him throughout life.
Please keep posting - I don't have all the answers, but I am happy to listen if it helps.