"Agreed, it has to be technique." -Aztec

Yep, get yrself a good swim coach. Get video taped underwater. Swim a lot with a lot of drills thrown in to help you roll your hips, keep your elbows high, develop your catch in the water, and do plenty of catch up stroking so you get a feel for gliding in the water and not struggling or fighting with the water. You've got to think like a canoe.

One week ain't enough. Plenty of practice (and real consistency) over several months (and longer) will allow you to see noticable improvement.

Remember: there is no "off season" with swimming, you gotta do it year round and learn to love it (sort of).