Endometriosis isn't diagnosed by a blood test, it is diagnosed by a Gynaecologist during a laparoscopy (like keyhole surgery with a tiny camera). A trial of a contraceptive pill can be a reasonable first step though, although obviously this hasn't helped you.
There can be other causes of severe pains, I would see a GP and ask whether they think it could be endometriosis or something else. Have a look at symptoms of endometriosis first and write a list of those you have, and keep a symptom diary to see if they are worse during your period, or with anything else.
Blood tests would be helpful for irregular periods looking for polycystic ovarian syndrome, thyroid probs amongst others.
Many GPs don't contact you with blood results unless they are very worrying- they ask you to telephone for your result. They might be sending off thousands of blood tests a month and can't phone everyone. Have you asked for your blood result?
If you don't find your GP interested, you could see a different doctor- do any GPs have an interest in women's health, or the qualification DRCOG (a Gynae qualification for GPs), or if no other GPs you could push for a Gynae referral if your symptoms do seem to fit endometriosis.