stand straight lift your right knee towards your belly (are you falling to the left or do you have to put some weight on your left foot before you lift your knee?) Now do the opposite, left knee up. Any problems?

Chances are you have mobility/flexibility issues in your hips,

here is an amazing routine you should try everyday before bed, 10 minutes max

Episode 97/365: Hip Mobilty For Improved Squatting Tomorrow - YouTube

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I'm not making any diagnostic but poor hip mobility applies to pretty much everyone. This is safe for anyone so give it a try