Learning To Swim At Age 27

I'm 27 years old and very afraid of water but I've decided I want to finally get over that fear and learn how to swim. My only previous experience of being in the water was five afternoon swimming lessons through school when I was 11, couple of trips to the lake where I waded in up to my chest and stood around and 2 aquafit classes when I was 24. I recently signed up for lessons at the YMCA that are once a week for an hour, plus I usually go to the pool for a couple of hours on weekends. I've taken 6 weeks of lessons now and I've improved a lot but in some ways I feel like I haven't improved enough. I used to be afraid to even put my face in the water and after about 10 hours of pool time I finally figured out how to blow bubbles out my nose. I still haven't figured out how to blow bubbles out my mouth without inhaling water and I don't feel like I can blow bubbles or hold my breath long enough to even do a short front glide. I'm still afraid to even do a back or front float without assistance of some sort because I'm worried about my head going under. I've bought some nose plugs, but none of them seem to work very well for me. I've figured out how to tread water but of course I'm only comfortable doing that because my feet aren't far from the bottom and my head isn't underwater. I'm getting frustrated because I'm the only one in my adult class who seems to be afraid of the water to such a large degree. I've signed up for an additional set of lessons to the ones I'm taking now, but I'm worried that I'm not going to improve significantly because of my fear. My fiancee's sister is a lifeguard and she says I could be swimming laps by next summer but I'm not so sure. I know a child who isn't afraid can learn quickly but I'm not so sure about myself. I was hoping that someone here might have some advice or encouragement on how I can become more comfortable in the water and give me some idea of how long it should take an afraid adult to learn how to swim. Thanks.