How can i keep myself motivated to exercise by myself?

Several ways!: Listen to invigorating exercise music-dance, or something made specifically for exercise. Exercise at higher intensities for briefer time periods, such as 15m per session, very hard! 5 x /wk, vs 45m x 3/wk. Going hard for brief periods of time is mentally easier than longer periods at lower intensity. And finally, do things like stair climbing at work, walking whenever possible during the day.