@birthmother I am so very sad to hear about the loss of your grand-daughter. You pose the question of whether you are mentally unwell or sad. My personal view is that as a society, we tend to pathologise sadness and grief, but I accept that others will hold different views. Sadness and grief are totally normal responses to loss.
Of course, it is entirely possible to be both sad and mentally unwell; people with a mental illness experience sadness, and sad people can have or develop a mental illness. Sometimes when we are very sad for a very long time, it changes the chemistry of our brain and this can lead to depression. Thus, while grief itself is not a mental illness, if it continues unabated for a long time, it can lead to depression.
As to "what happens" if you self-diagnose yourself with cptsd, well, nothing really "happens." It can provide a valuable starting point for figuring out the way forward. For example, it might inform the sort of therapist you might want to try connecting with, or it might help you to find useful resources such as books or support groups.
There are quite a few people here in Forum Land with cptsd, so I hope you are able to feel supported here. 