When I download my dives onto the computer, I can see a direct correlation between my buoyancy and my breathing (SAC rate.) When I breathe faster, I go higher. The more relaxed I stay in my breathing, the more neutral I stay in my buoyancy. Best cure for this - diving. Just keep diving, work on relaxing and it will come. 15 feet to the surface are the hardest to control but it will come! :)