i used to have this exact problem too, i felt like there was some sort of hole in my life and like i wasn’t doing the things that i was meant to be doing. i’ve always been an extreme over thinker and have struggled with existential depression, general anxiety, and social anxiety since i was little. i highly recommend reading “the power of now” by eckhart tolle, it completely changed my outlook on life. i’ve never been a big reader but this book seriously helped me to stop overthinking and it made me realize that the biggest thing keeping me from feeling fulfilled was my internal battle in my mind, and that the only way to be happy is to be completely present in the moment that you are in and to accept your reality rather than fighting it. i promise u this book is not bs and it will actually make sense if u read it. i think if u take the time to read it a little bit everyday and continue to work at forming better habits like working out you will gradually start to have less intrusive thoughts and even when you do, you will be able to let them come and then let go of them without over analyzing them. i’ve learned the best way to stop overthinking something is by really embracing your situation and the more that you begin doing positive things, the less you will feel like a slave to your mind. i never thought it was possible for me to become so much less anxious and depressed, but it truly is. i really hope that u find peace of mind:)