What are some techniques to stay positive during work hours?

Focus on your goals. Add confidence to your skills with training you might need.
Stay out of the negativity circles of gossip. Ignore comments that are not helpful. When supervisor gives you critiques, listen and nod and say ok. Take the comments and use them. Always conduct yourself professionally. At least 3 times a day; Take 3 deep breaths and breath out slowly and say I take care of things, people, places I can control. I give things I have no control over to the Higher Power.

Your question is telling with "I lose my mind." You can "train your brain." First, what do you really mean when you say Lose my mind? Disect that phrase and write down what you discover. Address those issues. Second, choose your words carefully. Change your lingo to positivity. Invent a safe place in your mind with your creativity. Your safe place contains geography, colors, aromas, tastes, sounds, and your favorite music. Focus on this safe place when you start to get negative. If you can't do this alone, ask for help. Contact a counselor or mentor.