You may notice that your left side (or, if you're a lefty, your right arm) is weaker than your right while grabing a pair of dumbbells.

And It's common for people strength difference between their side.

We often use our dominant side far more than our weak side.While we wouldn't necessarily consider this every activity exercise, the more we repeatedly use one side, the more efficiently our brain learns to fire to those particular muscles. This results in stronger muscles on that side and quite often larger muscles as well.

You can also try unilateral training and exercises, like single-leg lunges, single-leg squats, single-arm shoulder press, single-arm chest presses, and single-arm rows. Adding these body weight leg exercises to your routine.

Your weaker side will catch up naturally since it will be forced to work harder.