You're doing it wrong.

Exercise can certainly be tiring, if you're training for performance, or rehabilitating an injury. But, a basic yoga class, a few laps of the pool, or walk around the block isn't going to noticeably tire an otherwise healthy adult.

Time-consuming? That's likely short-sighted when you account for reduced longevity, time spent ill, etc. A few hours a week isn't that much time in the overall scheme of things.

And exercise should almost never be painful. The only exceptions would be rehab or training for a specific event.