Buckling of your knee under your weight is called instability and  points toward a ligament tear.ligaments like (but not limited to) acl ...could Tear under extreme force in young people and it is important to reconstruct them otherwise apart from the problem of instability you will end up damaging the knee cartilage and menisci. This is not something you should ignore or wait for it to heal because a complete tear will not heal. However this is all speculation at this point because no one can give you a diagnosis without examining you clinically and probably getting a mri later.