This is because you are not circumsized. The head of your penis has always been protected under your foreskin. As a result, it is extremely sensitive. This is normal and has both pro's and con's. The pro is that sexually you receive a lot more stimulation than a circumsized man would. The con is that you will likely reach orgasm a lot quicker, whereas the circumsized man receiving less physical stimulation could hold out a bit longer.
In either case, this is normal, it's healthy and it will go away in time. Yes blowjobs can become a little painful if she pushes your foreskin back... Like a sharp pain. But it will go away in time as your body gets used to it.
Many women experience this as well. Some have a foreskin that covers their clitoris. If the clitoris is touched directly (the hood pushed back), she can feel immense pain. Whereas other girls who have been more "experienced" in this type of touch, or who doesn't have as large of a hood protecting her clitoris will not feel that sharp sensation.