yeah i think what's happening is you're getting really tensed up. also, is your boyfriend an above average size? because that can be part of the issue. i agree with elphaba that your gynecologist could have some good tips for you on how to lessen the pain or maybe a procedure to remove the hymen. or she might have some topical pain reliever you could use.
other than what the other gals here have said, my only advice is to make sure you're comfortable with it, relax, and even if it hurts some, keep going and the pain shouldn't last very long before it starts to feel nice
good luck!