Torn muscle

seeled

First of September I tore my rectus abdominal muscle (lower stomach) doing push up (Yes, push ups). I got medical clearance first part of October to start doing them again. However, when I do them, I have the same pain higher in my stomach now like I am about to tear another stomach muscle. What can I do to strength them? I have been doing planks and stretches on an exercise ball. It is been over a month since I got medical clearance! I am afraid I will tear one again. That was the worse pain I have ever been in and do not want to go thru that again but I need to be able to do push ups again soon!!!