Hi, I'm a laboratory technician who works in all departments, including the blood bank. Getting your blood typed at birth is normal practice in some places, but not everywhere. In your case, if your doctors didn't anticipate you imminently needing a blood transfusion, they probably didn't order a type & screen (the test that will tell you your blood type, as well as find possible antibodies that could cause a transfusion reaction). If they were concerned, they might have ordered a blood bank "hold," onto which they could add a type & screen later, but a hold by itself won't get you your blood type either.
I don't know the regulations elsewhere, but in some countries, including the United States, where I am, your type & screen "expires" after a few days, and it will need to be repeated before you get another transfusion. We also will never, EVER, UNDER ANY CIRCUMSTANCES, transfuse type A or B or AB blood into your body going only on your word (or anyone else's word, or an ID card) that you know what type you are. We test you. Every time. And until we test you, we will only give you type O, because that's the only type that won't kill the other types dead if they get the wrong one. This is why for us there's not really any point in knowing your blood type ahead of time in case of an emergency; the testing will still need to be done before you get anything but O. And then, 3 days later, the test will expire, and if you still need blood, you'll get tested again.
We do all this because Shit Happens - someone screwed up your test the first time, the wrong patient's blood got labeled as yours, you were carrying a fake ID when the ambulance brought you in, you developed a new antibody since your last transfusion, your blood type CHANGED (rare, but can happen), etc, etc - and the blood bank is the only department in the lab where if enough errors go unnoticed, we can directly kill a patient.
So, depending on where you live, this is possibly why you don't know your blood type - whoever treated you never ordered it because they didn't expect you to need a transfusion (a surprising number of surgeries are pretty light on blood loss these days, actually), so there was no reason to test you at that time. It's also possible it's suppressed/not visible to patients in whatever system they use.
Outside of needing a transfusion within the next 3 days, your blood type isn't very useful information, medically speaking. Some doctors will order your type for you if you ask, though.