Kat,
I didn't read all of the responses very carefully but I have something to add. It's possible I'm repeating someone.
1) First of all read and re-read Walter's post.
2) You don't need other gear. People who suggest buying different gear for a skills related issue usually don't have the answer. If you buy a new mask, you'll still have this problem.
3) Once you get this down you should be able to clear a 1/2 gallon milk-jug with 4 breaths. All modern masks are low enough volume that one breath is sufficient.
I'm just guessing here, because I haven't seen you in the water but from your description I am *guessing*
a) that you aren't looking up high enough
and
b) that you're probably losing air you exhale either through your mouth or by lifting the skirt of the mask and both letting air escape plus "scooping" water.
The solutions to these problems are easy. For (a) just consciously look up until you see the surface of the water. If you're doing the skill while horizontal and/or swimming you might need to just move your head back as far as it goes and possibly slow down and get a little bit (don't over-do it) vertical.
The solution to the other problem is to not pull the mask off of your face. All it takes is one finger to hold the mask against your face. you place the finger at the top of teh frame between your eyes. Just hold the mask there, don't *push* it on or it will deform the seal and probably result in leaks. Just hold, don't push. If you're thinking "the water won't get out if you do that" then just try it. The water gets out.
To avoid losing air through your mouth push your tongue up behind your top teeth. For most people it's like a miracle. You'll immediately stop exhaling through your mouth.
Good luck.
R..