Aw! Sounds like he's really overwhelmed! It's a really tough time for kids that age. Don't worry. I think probably flipping through a good discipline book will be a big help.
There are some very positive, sensitive books out there that really open parents' eyes up to what's going on in their little heads. Happiest Toddler on the Block is great. So is the Sears Discipline Book, and I've also found Easy to Love, Difficult to Discipline by Becky Bailey to be an absolute Godsend.
Believe it or not, you might also benefit greatly from BabyTalk, a language program for babies at any stage of language development. They found, along the way, that babies' frustration was greatly eased when parents did the babytalk program with them, for two reasons: for 1/2 hr each day, one parent spends 1-on-1 time Letting the Baby Guide the Focus of Attention. This is huge for a baby, who's just leanring to stretch that attention span. Having it directed all the time is very difficult on a child: look at the ball! Look at the doggie! Can you say "apple?" Let's do this! Dont' touch!" Their already-fragmented attention can't handle it, and it's overload. Let him do whatever he wants with his toys, etc., and play with him, but just do a running commentary, voicing what you think he might be thinking, for 1/2-hour a day. You will see immediate improvement.
The other reason is, learning how to talk is so empowering. Over *time*, as your son gains in vocabulary, he won't be so frustrated all of the time.
Meanwhile, you might also consider learning baby sign language together, for the same reasons.
Knowing great tips on how to prevent, how to nip in the bud, how to get through, and how to recover/provide guidance and/or some punishment after temper tantrums is GOLDGOLDGOLD. Don't just ask friends' and family members' advice. I've found all too often that, as well-meaning as it is, it's just a case of the blind leading the blind.
I can't go too far into it, but to tide you over till you can get one or more of these books: when he just *begins* to get upset about something, show empathy. Use very short, very simple sentences that show you understand what he feels: No diaper! No diaper, no!, etc. Express concern when you reflect back his feelings, instead of sounding angry, yourself.
WHen he is hitting, lovingly but firmly hold him in a way that prevents him from doing harm. TEll him you love him but he may not hit.
He might not be too young to be taught to carry around a little stuffed animal or a soft ball that he can throw as hard as he likes at the ground when he's mad. Show him this when he's in a good mood :) So he has the patience and wherewithal to understand.
Make sure not to make too many demands on him later in the afternoon/day when he's likely to be tired and overwhelmed by all that he's taken in that day. Shopping, visits with friends, errands, etc. can wreak havoc on him, and of course you and everyone else, after 2-3 in the afternoon.
Make sure he's well-rested in general. No-Cry Sleep Solution has charts for optimal amounts of sleep and when, and great techniques for maximizing babies' rest - and parents' too ;)
Note whether he is eating/drinking more than just a few, light, very small amounts of sugary foods/drinks per week. Sugar really can completely overstress little ones.
But really, I think the best thing is to do a little research on discipline. There isn't a whole lot out there for such little ones, but I've found the three that I mentioned, above, to be really great.
