Hello and welcome to HCM.
Thank you for your query.
Both your daughters are growing up and experiencing symptoms of a menstruating adolescent girl. Although, the fact that the older one is irregular with her periods, could be a small cause for concern. I would like for you to visit a doctor, and get her checked up. As
irregular periods, right from the start could be a sign of various conditions that could result in permanent irregularities in the menstrual cycle.
Abdominal pain and lower back pain in the younger one could be the sign of an approaching menarche, unless she has other gastrointestinal symptoms like vomiting, diarrhea,
constipation, nausea, chest burn (
heartburn), belching, etc.
Both your daughter's are growing up, and hormones bring in mood changes, changes in the body, pain and changes in the body (including the breast).
The presence of pain under the breast of the older one could indicate
costochondritis or even Tietze's disease, which is quite common in young women, but it is a very distant assumption. I would request a chest x-ray, just to be on the safer side, and if inconclusive, an abdominal
ultrasound as well. They might report normal results, and if they do, you can blame the pain on the
menstruation. Do not worry, I am sure they are both fine.
I hope I have succeeded in providing the information you were looking for. Please feel free to write back to me for any further clarifications at: http://doctor.healthcaremagic.com/doctors/dr-shoaib-khan/64581 . I would gladly help you.
Best wishes.