Yes, it is really difficult, I must admit. Positivity comes with your personality while enhanced by your social circle.
/ The right crowd
Just being with a person who is enthusiastic about living life is enough to spur you. This person will let you discover that the grass is always greener on the other side. This person also lets you realise that not everything in life goes your way, and makes you accept it.
/ Learn some humour
Everyone can use a good laugh to have their mood liven up. Bringing laughter to people around you can actually make you feel even better, because you know you've brought happiness to them, and that's really crucial. Learn some humour, don't take things too seriously, make a joke out of yourself, be foolish for once and be daring.
/ Treat yourself
Everyone can use a treat (by themselves); to really spend time doing your favourite thing. It could be reading a good book, eating good food, listening to a good song nobody appreciates, playing that video game you've always wanted to get your hands on or even just buying yourself some new clothes (or shoes!). I mean, after all those hard work, surely you could spend some money on yourself right? These would be the little things you would be looking forward to in your life.
I call it the me-time.
Keep on musing