Would a 4-5 cm Diastasis Recti cause pain?

Diastasis or separation of the rectus muscles is quite common and rarely would cause pain. This is commonly associated with weakening of the abdominal wall muscles and the fascia or tissue that supports these muscles. When severe this can contribute to more bulging of the relaxed abdomen and more pressure on the lower back. Start with an assessment by your primary care physician who may be able to determine if you should see a Plastic or General Surgeon to give you specific recommendations. 

Most patients do not complain that their abdominal muscle separation causes them pain. Pain associated with abdominal tension would more likely be related to a hernia or muscle strain. The diastasis is just a weakening of the abdominal wall that results in a loss of strength and contour of the abdominal wall. It usually is painless.  

Hello. Your diastasis shouldn't give you pain, it could be uncomfortable, but should not cause pain.

I think the answer is probably no, it is not causing pain, at least I have never seen it be symptomatic over 3 decades of practice.