Negative thoughts aren't necessarily bad. Obviously these are concerns that you have. It's all right to give them some time in your head. When you feel negative, check in with the "HALT's" to see if you're also Hungry, Angry, Lonely, or Tired and deal with those first, before you even start to focus on the negatives, make sure you're not just needing a snack or a nap. It sounds silly, but can make a big difference in your mental attitude when your body is feeling run down. Maybe set aside some time during the day to give your concerns some "face time" and five or ten minutes to recognize that these are things you worry about. Set a timer. Once your time is up, write down some positive thoughts about these situations, thir has some very good suggestions regarding those, ways that these situations can be positive. Writing them down sometimes helps to focus on these positives as more real that your thoughts, which you have allowed to be fleeting. Practice with this will eventually leave you with a list of positive possible outcomes, while the negatives will have been allowed to be seen, and let go.