Can you get endometriosis after having a baby, if you never had it before?

Any time: Endometriosis can present at any time in a woman's reproductive lifetime. Diagnosis of endometriosis does not have any cause-and-effect relation to having had a child. Women with endometriosis fairly obviously have the disease before a diagnosis is made; it is sometimes difficult to say how long disease has been present when it's first diagnosed.

Absolutely: It used to be taught that endometriosis patients had not only pain but infertility. However I have seen many patients who had neither and were still found to have significant endometriosis. The only way to confirm - and properly treat - endometriosis is to perform excision (surgically cutting out) of the implants or nodules using laparoscopy. This provides visual/pathology confirmation.