I had a similar experience when I started using my drysuit. The drysuit course was in freshwater and went well but I didn't have many undergarments on. Diving in salt water (Queensland, AU) it was extremely difficult - floaty feet, head down which was very frustrating. I had to readjust my weight and started using a weight belt (rubber type) in addition to my intergrated weights (Wing BC). As I dove more it became much more comfortable, but it took around 6 dives to get to that point. I was also able to drop some weight as the number of dives increased. Currently using 24 Lb but still feel like I could drop some weight (~25 dives). I only need 14 lb with a 5mm suit so this was considerably more weight than I was used to.
I use my BC for buoyancy and only add enough air to releve the suit squeeze. I realize this is an old post but I couldn't find any help when I was having difficulty, so hopefully this can help someone else.