Hello....I'm also 18 weeks and I have been feeling my baby move since I was around 16 weeks so it's possible that you are starting to feel your baby's movement. I just don't believe that should be causing you pain. But I to feel discomfort and I feel like my baby is stretching which causes it as well as everything else stretching preparing for my growing baby.
No, you shouldn't feel any pain What's so ever, but im not ganna say it's not. Usually the average female feels the baby start moving and kicking @ 20 and upp
But if it is congratulations (: