I have low titer for rubella and hep b. they said my hep b was 5 and should have been 10. does this indicate some kind of immune disorder?

No: Were you checked to see if you were vaccinated? Did they check your surface antigen? This could just mean that you need the Hep B vaccine. Talk to your doctor further about this. Best wishes.

Vaccinations: No, this drop in immune titers does fall over time depending on when the vaccination was given or that your body did not fully start producing these immune titers which is also common. You would benefit from getting booster vaccinations which will help your immune system re-evaluate those antigens and produce more antibodies against them.

Not likely: It likely means that your immunity produced by vaccination as a child is waning(decreasing). Not particularly uncommon. It's actually possible that even with your vaccination as a child that you may not have generated a significant immune response at that time. You may just be one of the many persons who doesn't produce a strong immune response to the hepatitis B vaccine. Best of luck.