I can't enjoy things like I used to.

I don't really now how to explain my problem, by I will try my best. So for quite some time already, I realised that i can't really enjoy anything in life. For example i want to go outside, enjoy the weather. I go outside take a walk, but I always feel like i'm not getting enough of it? I don't even know how to explain it, it feels like i'm always focused on something else, not my surroundings, that I want to enjoy. Another example: I am waiting for some big event, it finally happens and I'm kinda enjoying it, but also quite overthinking, being little anxious about it too. And after it ends I'm like: that was so cool, i wish i could relive it once again! Even tho it didn't feel like it while it was happening... Not to mention that everything flies by so fast, which i kinda understand, because as we get older, time gets faster (maybe that's why I'm having this problem, who knows?) but I'm just 21yo and time is already flying WAY too fast. And that's mainly it, I hope that I explained my problem as accurately, as it is.