How can i get myself to have more positive thoughts?

Practice: Understand that you have a choice of what to focus on or emphasize. Just as you can switch tv channels, you can also change what you place your attention on. It can also help to be more scientific or fair with the use of your attention. Give equal time (or more if possible) to appreciating, being grateful, celebrating vs. Complaining, resisting, rejecting. This probably will help.

Gratitude: I agree with dr. Smith about where you place your focus. "energy flows where attention goes." this means that you strengthen what you place your attention upon. One practice you can institute is some brief writing before you go to sleep each night: list 5 things you are grateful for. This helps re-direct your energy & thinking towards positives in your life. Can review them in the A.M. Too.