Yes, do get a prescription for something. Be aware that it will affect how you feel the first day (or even the first couple of days) after you arrive, along with your having jet lag, so you need to be prepared for feeling very "off" but it beats freaking all during the long flight.
Also, along with your husband, research the statistics on flight safety compared to automobile safety. I know you already know this -- you are statistically safer in an aircraft than you will be the next time you get into your car to drive a few blocks later today.
That kind of factual knowledge helps some people more than others. If your anxiety is irrational and not helped by that kind of knowledge, you may need to have a few sessions (not a lifelong commitment to therapy) with someone professional. Don't be afraid to see a therapist "just" for this fear. it really is not uncommon for people to see a therapist for a single issue like this, if that issue is so serious that it is compromising their ability to do things normally. Imagine yourself getting to the airport and freaking so badly that you don't get on the plane -- the impact on your marriage would be real and serious, so you need to deal with this now. You have plenty of time to work on it but don't try to do it all alone.
(By the way, if your husband is supportive that's great -- but if he's the type who makes fun of your fears or tries to "jolly you out of it" by mocking the fear -- he needs to hear from your new therapist that he has to stop that. Just saying.)
Also, can you try to take some trips involving flights in 2014 and 2015? Exposure to flying would help. You do mention that you can cope on two- to three-hour flights though it's not fun; look into taking a few trips that require you to fly. Expensive, I know, so it may not be an option but could end up making it better.
And be sure to load up on a million things to do during the flight JUST in case you are so tense your prescription takes time to kick in.
I also hate to fly, fear it, and have claustrophobia as well, plus we travel each year to Europe and there are always terrorist alerts at the airports and that makes me very jumpy (less of an issue for you heading to Australia). Those are six- and eight-hour flights and the latter is especially loathsome to me. But I love BEING at the destination where our family is located, and I know that my going means my husband and daughter have a good time, so I get through it. It IS hard, I agree. But you can do this. I really do recommend that if statistics and more flying don't help, you seek a therapist -- there are ones who specialize in helping people cope with specific fears and you can probably find one who has done work with people just on fear of flying. Good luck.