One of the side effects of Diastasis Recti is back pain so yes you can have back pain which is sometimes normal when you have Diastasis Recti.
I know I had back pain for awhile until I got rid of the Diastasis Recti so it's usually nothing to be worried about and another side effect of Diastasis Recti besides back pain is constipation as well as incontinence or urine leaking.
Diastasis Recti will usually go away on it's own within 6 months however if you want to get rid of the Diastasis Recti faster you can have Diastasis Recti surgery.
The surgery for Diastasis Recti is pretty expensive but well worth it the money if you can afford to have it.