How far along are you?
I'm sure it's probably paranoia. I do the same thing, worry about every little thing. :) If there's no bleeding, the cramping is probably unrelated to the flu shot & more just growing pains, I would say.
My doctor recommends the flu & the pertussis vaccination & I have yet to do either. (Not sure when exactly you get the pertussis one, if it matters or not when you do it, actually)