I suggest you get your blood retested or check with parents to be sure (tell them your blood type). If your mom is O+, then you most likely should have gotten O, O is dominant. Or you should have been an A+ from your dad.
If your dad was A+, it is possible that he is actually a AB+ (or one of your parents is maybe not your bio parent), which is where you could have gotten the B from. Since both parents have the Rh factor of +, then that is why you you are +.
Parent 1+parent 2=child
A+O=A or O (you should either be an A or an O, unless one parent is not you bio parent or you were adopted).
B+O= B or O
O+A=O or A
O+B=O or B
A can only donate to A and AB types. B can only donate to B and AB. AB can donate to A, B, and AB. O can donate to A, B, AB, and O.
Recipients: A can only receive A blood type. B can only receive B. AB can receive A, B and AB. O can only receive O.
Same concept applies to the Rh factor; + can only receive +, - can only receive -.
If people receive a blood type that doesn't match their own, their own body defense attack because of the antigen (body will recognize the antigens as foreign). Rh factor differences can be dangerous, especially for pregnant women.
Considering yours is different from either parents
Blood type A has the a-antigen. B has the b-antigen. O has no antigens. When they check to see what blood type you have, there is a serum they use.
First they have 3 slides (the ones they use in science experiments).
1st slide has a drop of the a-antigen serum.
2nd slide has drop of b-antigen serum.
3rd slide has the Rh factor serum (+ and -)
Drop of your blood is placed in each of those slides with the serum and mixed.
If clotting occurs in the samples (they look like little dots), then there was a reaction to the serum. If reaction occurred in both a and b antigen serums, blood type is AB. If it only occurred in one (a or b antigen serum), then your blood type is either A or B, If no reaction, then blood type is O.
If clotting occurs in the Rh factor slide, then your Rh factor is positive (+). If no clotting then you are Rh negative (-).