Is it obligatory to perform ghusl due to post-menstrual discharge that is mixed with something resembling a strand of hair or a thread, and there is doubt as to whether it is semen?

It is clear that you are afflicted with waswasa (obsessive whispering). We advise you to ignore these whisperings and turn away from them. If you see the sign of purity, do not trouble yourself by searching whether anything has exited or not; rather, build upon the original state that nothing has exited from you. And if you doubt whether something necessitating ghusl (ritual bath) has exited from you, the original state is the continuation of your purity, and that nothing has exited from you. Leave these whisperings and do not pay attention to them, for yielding to waswasa leads to great evil.