Ob-Gyn questions? Ask a gynecologist online.
Yes, you do need to see a doctor.
What probably happened is that you had a spot of infection in that area after the CS. The infection cleared up but an empty space remained which then became covered by thin scar tissue. This gave way when you rubbed it.
Your doctor will need to assess how deep the open space is and the integrity of the scar. You may not need any treatment if the empty space is quite shallow but if it is deep, you may need it to be sutured .
Since there was bleeding, there is also a chance of an infection.
Please see a doctor as early as possible.