Stomach pain for 4 year old. Recurring!

My son always complain about stomach pain at night before sleeping and early morning ( but doesn't cry at all, it is not severe though.he says stomach ache for few minutes and then plays normally all day). He was complaining from last month. We have reached out pediatrician and he suggested us Abdominal scan and we have done it twice , first it came out as multiple mesenteric lymphonode and second time it came out as Cysistis ...my pediac then suggested to go for Pediatric Gastrointestinal ...he suggested us to get plain abdominal xray..after seeing it , he said it was constipation and filled with gas...My son suffered with constipation last year for around 6 months and it was cured..and as far as i know, the kid will pass motion once in 4 days or more and with lot of pain..but now my son is passing motion daily without any pain. Not able to understand the problem..Can someone please help me out on this. PS: He never cried about stomach pain..it last only for few minutes, but recurring