What Causes Continuous Stomach Pain?

Hello. Our daughter just started her periods in October. She is 12. She now suffers with continous stomach pain. The symptoms are - 15 mins of no discomfort whatsoever. 2 to 3 mins severe pain, then returning to 15 mins no discomfort - and so on. This situation has been the case for 8+ weeks and it affects her 24 hours a day. She is on strong sleeping medication so she can actually sleep. After weeks of doctors and consultants - we have no answers. Any help appreciated.