I don’t think one can completely eliminate stress, but can reduce it or manage it. Exercise (cardio, and weight training) can help. If the negative thoughts are pretty interfering, you can go to a therapist, preferably one who is a cognitive-behavioral therapist. It wouldn’t hurt just to go one session & see what’s up. You can read a couple books too, “Feeling Good” by Burns or “Get Out of Your Mind & Into Your life” by Hayes. But exercise can help a lot.