13 days post op Breast Augmentation, sudden potential muscle tense or implant moved, or maybe normal?

At just 2 weeks post-op and under the muscle, it sounds like you are experiencing a muscle spasm which is not uncommon.  Definitely call your surgeon to let him/her know what is happening and see what they recommend.  I typically prescribe a muscle relaxer for my breast augmentation patients for this exact reason.  ac

Also it sounds unlikely that anything untoward has occurred, the only truly acceptable reassurance will come from your surgeon, who may well ask you to come in for an examination.  All the best. 

Based on your description you may be experiencing muscle spasm if your breast implants were placed beneath the chest muscle.  This is not uncommon early after breast augmentation.Gentle pectoralis muscle stretching exercises by lifting your arms up from your sides can be helpful.However it is important that you see her plastic surgeon for an examination and reassurance.