Complex PTSD is very complex! I am sorry you are having your diagnosis questioned on here. The poster is right that C-PTSD isn't in the DSM but many many therapists and mental health professionals give this diagnosis out of the USA and in the USA (as yours does!).
The reality is that the DSM-V doesn't decree reality. People are complex and people with trauma histories are even more complex. The cumulative affects of developmental trauma are just what they are... and the DSM-V is a guide that has sorted psychological and mental health symptoms into categories.
Many therapists fought hard to get the diagnosis of C-PTSD included in the DSM-V because there is not any other diagnosis in the DSM-V that describes the cluster of symptoms often found when human beings develop and form their very selves in conditions of interpersonal trauma. The DSM-V gods (why oh why do I imagine them to be a cast of elderly white men?) decreed it Should Not Be. They thought the symptoms could be described by other disorders.
Still, many intelligent and informed trauma therapists very professionally use that label because despite the DSM-V gods being ^%$#*$ they realise their clients cluster of symptoms are best described by what many many trauma therapists have collectively described as Complex PTSD. Just as your therapist has evaluated you and decided that your collective symptoms are best described as the condition collectively decided upon as being Complex PTSD. I am glad you have a therapist who is knowledgeable about trauma and its devastating affects. I am sure your therapist is not at all ignorant about diagnoses or the DSM-V and I wish you well on your healing journey as you navigate the complex waters together!