In general I go by the reasoning that if I don't enjoy something, there better be a good reason that I'm still doing it. I'm fortunate enough to really enjoy electrical engineering and have a good job lined up down in London for September but I treat my career as a means to living a good lifestyle and being able to do other things that I enjoy while not working.
I'm currently make the most out of my last few months of University (read: causing as much trouble as possible), juggling uni work, paid work and being involved with all the social/society stuff that makes life interesting (and probably drinking too much!). It's very very crazy busy but that's how I like things, I get very bored if I'm not doing something all the time.
More generally, it is entirely up to you with what you do with your life and only you can change your internal mental state to progress onto better things. I think deciding to do something, difficult, different or just interesting, in your head (of your own will) then going and doing it is the most satisfying thing in the world. Whether it being washing the dishes or moving to a different country.
I would also say that life is more generally about balance, you need to do less interesting things/hard work/have a job so that you can enjoy other things. The contrast and variety between different things needs to be there otherwise your life just blurs into a constant of something (good or bad).
Volunteering is great, I spent a really enjoyable week helping to replace track and sleepers on a steam railway where we were essentially free manual labourers. Lots of heavy lifting and shovelling but at the end of the week we went all the way up the line in a diesel engine (to do more work) but that made it worth it. Ultimately it's not something I would want to do all the time but an interesting and different way to spend a week.
I also find it very easy to not worry about things. If there is a problem I just think it through thoroughly and if I can't do anything to fix it, I can generally just accept that or get help from someone. Busy is fine, stressed because you don't have time to think/plan everything is not. However a positive can-do attitude will work magic for just about everything
