Do I have Divarication Recti? Could it be caused by previous surgery?

You may have a diastasis recti, or separation of your abdominal muscles.  It is possible that you have a hernia as well.  A plastic surgeon could definitely tell if he or she could help you by examining you.

What you are referring to is what we call here in the US as diastasis recti which is a separation and weakness of the abdominal wall between the two rectus abdominus muscles. This is often caused by weight gain or child birth. This is not a true "hernia" but a severe weakening of the fascia of the abdominal wall between teh muscles.  From your description a hard lump in the center of your abdomen when doing a sit up could be diastasis recti (rectus diastasis), but more likely is a recurrent ventral/incisional hernia or possibly bulging of the mesh if may have had placed at a prior hernia repair. If you see a general surgeon or plastic surgeon it is likely they will be able to tell the difference. Also tests such as an ultrasound or CT scan can sometimes demonstrate if what you have is a true hernia or just diastasis. I hope this helps, best of luck.