Hi Melinda, Yep it can be extremely wearing to have to listen to whinging, grizzling and/or tantrums. Remember that most, if not all, children will go through stages like this, so it most likely isn't your fault. THe best way to handle it will depend on the individual child.

Strategies I have noticed DON'T tend to work well are:

Punishing the child - if he is unable to control his emotions, it is unfair to punish him for expressing them. If he is just out for attention, than even negative attention is a result, which could reinforce the behaviour. Although we do occasionally use a time out for things like hitting someone on purpose - but we try to do this calmly and supportively.

Ignoring it - lots of people say you should ignore all inappropriate forms of communication / interaction. I have a problem with this because it doesn't help the child to process his feelings, and it doesn't teach them more appropriate ways of behaving.
We are still very much working on the issue in our household, but we have found that the following things work (sometimes!)

Pay close attention to how your child is going. As well as making sure that you don't allow him to get too tired, overstimulated, dehydrated etc (which you probably already do), you will learn to see situations brewing before it gets to the stage of him whinging, screaming, hitting or whatever.

I try my best to get the kids outside every day in whatever weather. Ds has waterproof trousers and coat and gumboots, so even if it's pouring with rain, he can go and jump in puddles or whatever. I find his behaviour deteriorates dramatically if he misses outside time. (we're also lucky enough to have a verandah so he can ride his tricycle up and down there too).

I make a point of sometimes allowing him to change my mind by respectful negotiation. Although I only do it in cases where the outcome doesn't really matter, I thing it's giving him the idea that there are more effective ways to get his own way than by acting up.

With activities, I find we need to have a fine balance between novel or stimulating things and routine, calming things. I also find that they need to have some time to be bored and find their own entertainment, rather than always relying on mummy to initiate the next activity.

Also with ds I have started to talk to him a lot about emotions and acceptable ways of expressing them, practising how to ask for what you would like, and so on. I'm not sure how old Jacob is, but you could try and see how he responds. I think it takes a while before they really understand that hitting can hurt people, or even that other people actually have feelings.