Nearly every job has its drawbacks, but for more than half of U.S. employees, their current work situation just isn't cutting it. A new Gallup poll found that 51 percent of workers in the country are keeping an eye out for job openings or actively searching for new positions.

There's a high number of jobs currently open in America, but many employees are still dissatisfied with where they end up. According to Gallup's latest "State of the American Workplace" report, 68 percent of workers say they're overqualified for the job they have. And even if they aren't looking to switch jobs right away, that doesn't mean they're thrilled with their present situation: Only 33 percent of employees reported feeling engaged at work.

But it isn't just unsatisfactory job conditions that have employees itching to move somewhere else: They also feel optimistic about their prospects. Sixty-three percent of people Gallup surveyed said they think it's "very likely" or "somewhat likely" they can find a job that's just as good as their current position. Compare that to 42 percent who said the same in 2010 following the recession.

If you're an employee who's not ready to make the next step in their career, or an employer who wants to keep their workers happy, science can help. Studies have shown that employees are happiest and most productive when they have the freedom to work from home and schedule breaks throughout their day.

But there are some jobs that can't be improved no matter how much you change your routine. Look out for these signs when assessing whether or not it's time to jump ship.