Could I have ruptured a internal suture?

Thank you for sharing your question and I am sorry to hear of your stomach strain.  If your muscle repair suture had torn, pain is usually located over the middle of the stomach running somewhere from your breastbone down towards your pelvis.  With the development of a bulge and worsening pain I would be concerned for the development of a discrete fluid collection, such as a seroma or hematoma.  See your surgeon for an evaluation, they may have access to an ultrasound that can help identify the cause of your discomfort.  Hope this helps

You would have to be seen in person. If a suture of your plication tore the soreness often goes away after a few days.  Are you sure it is not something else like fluid?

After abdominoplasty surgery, it  is a little unusual to have a bulge on the side rather in the midline. The rectus muscle is plicated in the midline with sutures. If a suture breaks, it potentially can lead to a midline bulge. Please consult your plastic surgeon. 

I am sorry to hear about the problem you are experiencing.   Generally, the abdominal wall re approximation done during tummy tuck surgery is quite secure but disruption can occur.  This disruption may be associated with discomfort and/or a change in the patient's physical examination.  Your plastic surgeon will be your best resource when comes to providing you with a diagnosis, advice, and/or meaningful reassurance.   Best wishes.