After 3 girls I had a son, quite a shock to the system...the book Raising Boys by Steven Bidulph (sp?) helped me gain some insight into how they function and some good tips on how to cope with our little bundles of testorone. Recommend it to anyone with a son.
Sorry to hear how stressed you are. My boy started playing up at the same age - his 2nd birthday he hit every child and had to keep getting put to his room! The only thing i can say is remember how much you love him, focus on the good bits/enjoy them and deal with the unwanted behaviour the best you can. What else can us mums do? My health visitor has been really helpful too - maybe worth speaking to yours? Good luck.