7 year old pooping in pants

Hi,Thanks for all the replys...where do I start.....Yes we have talked about adoption before. We have childrens adoption books, and I bring it up when i can but try not to mention it alot...., I think it just finally clicked ,..what it really means and the social implications????I dont know?? .. The 2nd grade classroom project was family tree and where did you come from , what country did you originate and about grandparents and what country they came from. To be honest I thought it was too much for an adopted 7 yr old plus being the only adopted one in class. We did ask to not perticipate. The teacher didnt understand where we were coming from .....and we did the assignment and talked.She did say she doesnt want to be adopted and wishes I birthed her. I told her I loved her and wish I did too.Now a little History...We adopted her at 1 1/2 yrs old. In Russia at the orphanage, they told us she was potty trained....advice from our agency we brought diapers and put them on her. I think she was potty train around three..or three in ahalf, it was hard but I dont remember it being any harder then my bio-son who is now 16.The last year she has had accidents and we dont make a big deal of it Its just been the last 30 days..she as had some constipation through out the years and has had some very painful poo's...I think she associates a bowl movement with pain. I think she trys real hard not to go to the bathroom and the body kicks in and she poops in her pants. I dont think shes doing it to get attention like other misbehavior that she does ...I think shes trying to hide it. She will hide the underware and has smeard alot of poop on the back of a towl in the bathroom. On the back of it like to hide it ????? I tryed not to make a big deal of it....but she know now we are angry,she has to clean up and wash out the undies.....I thought after a week of that she would go in the toilet but she is still not making it.Anyways I'm at my wits end and feel like a terrible parent to her and think about disruption and feel like a bad parent and doing everything wrong.We are drinking lots of water and gonna call the doctor tomm morning and mental health advice. I dont know who I would call???Please only kind responses please .Cindy