Kim,
Sounds like you are doing fine. It takes time to make improvements that are noticable. If you can ride for 45 minutes comfortably now, I would suggest jumping that up to hour rides. It's only another 15 minutes, and I think you could do that without too much problem. After you are okay with that, maybe a couple weeks, try adding another 15 minutes to your ride. Etc, etc. etc. I don't know where you are from or if riding throughout the year is an option for you. If it is, you can gradually increase distance over the winter and be totally ready for spring. If not, do what you can before it gets too cold or snowy and then find a winter activity that you can keep in shape with. If you can do some indoor cycling, that helps. And in the spring get back out there, start out easy and gradually increase your efforts. I have always heard and read that it takes a good year of cycling to get your "cycling legs". Not sure what that means, but I take it too mean that your legs are accustomed to the motion of cycling, the muscles you need to develop are in shape to ride. You have a decent pedaling stroke (tho' that's something that can always be worked on.) In other words, riding a bike feels comfortable and right to you. I don't mean that to be discouraging! A year sounds like a long time, but it's really not. You'll be amazed at how much you will improve. And then you will be the one helping other new riders and welcoming them to a wonderful cycling lifestyle.
Time is a companion that goes with us on a journey. It reminds us to cherish each moment, because it will never come again. What we leave behind is not as important as how we have lived." Captain Jean Luc Picard