OK, I don't know who has been guiding you in sexuality and health issues, but you've been getting the wrong scoop from somewhere.
If you have been in an inprotected relationship for so long and not gotten pregnant, there could be two reasons:
1. You were very lucky and always had sex during unfirtile times.
2. You or your partner are not able to produce a child, either due to a problem you have in producing firtile eggs, or your partner does not produce fertile sperm.
You could also have a condition that prevents you from ovulating due to a previous illness or infection. This does not always need to be felt or painful, but still there.
The best bet for you is to see a doctor to reassure yourself that there is nothing wrong, or if so, that it can be treated.
You only have one body in this lifetime - and it will only be as good as you are to it. SEE A DOCTOR.
P.S. Just a little information - one main 'blood' problem with a fetus is if you are Rhesus Factor Positive and the baby has an RH Factor of Negative - and even this can be monitored and treated if evaluated by a doctor in the early stages.

Good luck, see your doctor, and keep us posted.