I'm age 35 and trying to get second child but try several months still can't success. It's related to my dairy food or my career?

Unlikely. In general your diet and your career, unless thay are very unusual, have little-to-no impact on your fertility. What is your career and what sort of diet do you have? At age 35 it is common and safe to try between 6 months up to a year before conceiving. Most fertility doctors would be pleased to help you anytime in the process.
Neither. If you had a baby, you are not infertile but it is an idea to follow basal temperature for best time to try for conception. Also see a doctor as we really can help.