Work on frog kicking. Get someone to show you a modified frog kick and use that.
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Go kick your instructor in the nuts and ask for a refund because he has "stolen" your money. Buoyancy is a basic but vital skill and the foundation for scuba.
I know its a lot of time and money, but I would seriously look at a Fundies class if you can't find a mentor to help you fix the problems you currently have.
A question related to this thread: approx how much weight should I add when going from a 3mm full wetsuit, to a 7mm full suit with a hood? I used 12lb with a full 3mm in Cozumel last fall, but am going in cold water in New England with a 7mm and probably a hood. Still salt water. I realize there are no hard and fast rules; I'm just looking for a ball park estimate. Both suits were/are new.
I know this must have been asked at least 731458 times in these forums, but a search didn't turn it up.
A question related to this thread: approx how much weight should I add when going from a 3mm full wetsuit, to a 7mm full suit with a hood?
Really hard to say without knowing any statistics about yourself - so use this at your own peril.
I use a 7mm and use 21 lbs in salt water - I am about 175lbs and 5'8" in decent shape. If I want to lay down on the bottom due to current in an inlet I may add another 5lbs to make sure I sink.