Based on the information provided, the scar tissue is prone for stretching forces and the pain is mostly due to that, you can consult the doctor who has operated and get a scar softening ointment prescribed.
Coming to the exercises part , visit a nearby physiotherapy clinic and you will be guided with core (isometric) strengthening exercises and the therapist will decide manoeuvres to mobilise the scar tissue , it should help with scar tissue pliability so that you can start with abdominal exercises (active) as soon as possible.
(Yes these complaints are usual in such surgeries)
Next Steps
Visit your doctor followed by consultation with a physiotherapist.
Health Tips
Try avoiding spine extension activities.
Olive oil application over and around the scar tissue can help (ease) with movements.