Sorry to point this out... but, as you are only at the planning stage, do you even have permission from the University to contact people to use as research subjects? It is my understanding (both professionally-based, and educationally-based) that research requires ethical clearance BEFORE potential subjects may be contacted. Furthermore, because the intention is to use people who are NOT students of the University as subjects in research, you should be utterly certain that ethical clearance has been granted prior to contacting potential research subjects. As a Psychology student, it is important for you to understand that research using human subjects may be a very sensitive issue - especially if these people may be disclosing sensitive personal information (such as experiences of Endometriosis and its symptoms). In the planning stage, it's not even clear as to how you would deal with HOLDING this information, or how you would ensure ANONYMITY of subjects.
Personally, I suggest a little more planning and detailed thought is in order - to ensure that you have water-tight methods for keeping sensitive personal information safe, ensuring anonymity, and to ensure that you have gained the required ethical clearance to go ahead with the project.
There are many women on this site who have Endo, and who are happy to talk about Endo. However, this is on a forum for women with Endo. Such conversations, when used as the basis for research, become altogether a different kettle of fish - because there are implications for research subjects in terms of breach of confidentiality, and of risk of harm. Perhaps you need to refer again to University guidelines? Just double check with your Tutors/Mentors to make sure that you are going about things the right way, and make sure that you have secured ethical clearance. Having the right approach now may well lead to a good mark for the dissertation. By contrast, failing to follow ethical guidelines may land you in a heap of trouble!
Good luck with it all.