Happiness does not come from things that are external to yourself. You need to figure out what "enough" means in order to find joy and live well.
When I was 20 (five years ago), I was constantly trying to do more. I worked two jobs and took six courses a semester, which became easy, so then I wrote a letter to the dean to let myself do eight courses a semester, and got a job with UNICEF so that I had three jobs at the same time. I slept on Sundays. Then that wasn't enough, so I decided to write a thesis... and on and on. I was only ever "impressive" to myself for brief periods of time, and then I'd quickly feel like I wasn't doing enough again.
This feeling of illegitimacy, of emptiness, pervaded every aspect of my being. I was constantly looking for authenticity and challenge. Traveling to a resort wasn't authentic in any way, so instead I would fly to a country with just a brief primer on the language and no plans and hitchhike and beg my way around, to try to find that authentic experience. Of course, that didn't last either. No country was ever poor enough, or dangerous enough, or obscure enough, and I was back on the treadmill again.
The problem was that these experiences depended on other people and things that were external to me. The only times that I did find happiness were when I'd trapped myself in environments of solitude, hundreds of kilometers away from cell phones where the only thing to do was to reflect and feel connected to nature. The key, and I've only realized this in the past few months, was to stop giving other things and people power over my joy.
So, if I could give 20-year-old me a piece of advice, it would be just that. Take joy in the things that you control by being honest and realistic, analyze all things to figure out what things you can't control (don't place value on those things), and for things that you have some control over (your mark on a paper, or your deadlift weight, or the treatment of the animals that you eat), figure out what parts of that thing you control, be honest and focus on those parts, and don't sweat the rest.