Find out if she was really pregnant or just trying to keep me?
No way to find out really, you have no access to medical records, and unless they did an autopsy that revealed she was pregnant, you can't know.
How do you propose doing that? A lot of failed pregnancies have no actual record. Unless you were legally married you have no right to her medical information.
That information would be in the autopsy report. You might be able to get a copy of it, for a small fee, through your area's medical examiner's office.
If you must know you could always look up her social media accounts and try to get chatty with someone she communicated with regularly.
You know, at this point it won't change anything so why pursue it?