nose keeps on dipping on bigger waves

Hi,
I`ve been learning to surf over the last few weeks with my girlfriend and thought i`d try and seek out a friendly forum to help us get better!
anyway, this wkend we went up to north devon to get some practice in - unfortunately it was all flat until yesterday afternoon when the waves got a bit better so we went out at woolacoombe.
all was well, managing to catch a few waves and standup successfully
then the waves got quite a bit bigger - i found that everytime i tried to catch the wave, the nose of the board would dip and the wave would crash down on top of me. It was as if the wave was pushing the back of the board up and the nose would then drop beneath the water and i was toast then!
i`ve tried moving back on the board but this does`nt seem to help with the bigger waves.
we`ve been using the foam boards and i was wondering if it`s anything to do with them - i was also pretty knackered having been paddling around happily for while -maybe i wasn`t paddling fast enough perhaps?
has anyone got any tips for this ?
thanks,
mike
I`ve been learning to surf over the last few weeks with my girlfriend and thought i`d try and seek out a friendly forum to help us get better!
anyway, this wkend we went up to north devon to get some practice in - unfortunately it was all flat until yesterday afternoon when the waves got a bit better so we went out at woolacoombe.
all was well, managing to catch a few waves and standup successfully

then the waves got quite a bit bigger - i found that everytime i tried to catch the wave, the nose of the board would dip and the wave would crash down on top of me. It was as if the wave was pushing the back of the board up and the nose would then drop beneath the water and i was toast then!
i`ve tried moving back on the board but this does`nt seem to help with the bigger waves.
we`ve been using the foam boards and i was wondering if it`s anything to do with them - i was also pretty knackered having been paddling around happily for while -maybe i wasn`t paddling fast enough perhaps?
has anyone got any tips for this ?
thanks,
mike