The proudest moment that I have had as a writer was when my very first book was published. I felt a huge sense of achievement because of just how much time and effort had gone into it, and to see it there on the shelves was a fantastic feeling. Since then, I have published a lot, and I love the sense of relief you get when you send the final manuscript in to the publisher.
Being a freelancer, it's important that I'm incredibly organised and able to sort things out on my own with regards to deadlines, so the fact that I am able to write books without procrastinating is fantastic in my opinion. I know many people who take decades to write one book, whereas I can write a full 100,000 word book in less than a month, including editing and proofreading. I'm very much an all-or-nothing kind of person so if I write, it's all consuming until it's done.
I want to be in your shoes, Gemma! For years I talked about the book I would write. Then I went through a period where I doubted I had a book in me. Since Feb or march, I have been writing my ass off and have written six, maybe seven full books. One took me two weeks so I get what you mean---when it goes well, it goes very well.
I have books out there but so far, no bites. I continue to write and to improve, I think. I am disciplined like I have never been before--it's great. I hope to see my book in print someday because to me, there is no cooler profession!
A couple of years ago, I would never have thought that this was something that I'd ever be capable of. I have always loved writing, but I always struggled to write anything longer than short stories. To me, writing up to 100,000 words about the same story was foreign to me. I didn't think that I had that much information to tell people! But I found that planning everything out helped, and setting specific times to write was great, too. I did it as part of NaNoWriMo (I don't know if you know that) and having that community to help me and encourage me was very helpful. I haven't made much money from my book, but it's enough to encourage me to write another one, and I'm now around 8,000 words into it. I know it's not much, but it's a start, and that's all I really need at this point!
If you really want to write, just do it. Life is way to short to end it thinking "what if". Go for what you want to do, and simply enjoy it. You've written, you know you can do it, so don't rest until somebody realises what you're truly capable of!