i had this problem with my current boyfriend. two years ago i couldnt feel him because he is smaller than the ex boyfriend. so he told me to kegel exercises, and it works wonders. now my honey is as snug as a bug inside me.
if you dont know what kegle exercises is, it's when you squeeze your vagina muscels it's like your stopping the flow of your urine.
you can do it ten times a day sitting down, standing up, riding in the car, when ever you want. if your not use to it that muscle may feel weak and it might feel like your squeezing your butt muscle. to make sure your doing it right you can lye on your back and put your finger on the outside of your vagina to feel you tighten your muscle.
i promise you this works, but you have to be consistent with doing it everyday.
try squeezing your muscles while he make love to you also, there will be a difference.