Out of water training for surfing is a subject much debated and there are many websites about surf exercising. Everyone has a view and mine is not necessarily any better than others. Obviously sorting out your back problems is a priority, so obtain specialist advice. Its possible you have a muscle imbalance or something. Jaffa is/was (I think) a chiro so might have some thoughts.
I think if you surf enough - 2X per week or so - then additional exercise is probably not going to add much, unless you are looking to go big wave surfing or turning pro and need the edge; but I am assuming this isnt the case.
Its a bit unclear what your current level of fitness is. You say you do a lot of surfing, but if you can't run 5km then your level of aerobic fitness is (bluntly) quite poor given your age. But that can be fixed!
Assuming you are coming off a low exercise/training base, then almost anything is good for the first 12 months. Anything you do will help your strength and fitness and there is no need to specialise your training towards surfing until you have a solid base. Once you are reasonably fit and reasonably strong, then you can specialise. Surfing uses so many muscles that you need to get all of your body up to standard before worrying about lats or triceps or whatever.
In my view, jogging is 'over rated' as an exercise, both for surfing and general fitness. C25K is great for learning how to run 5km, if that is what you want to do. But being able to run 5km is not really relevant to surfing - it wont hurt your surfing and better aerobic fitness is useful, but if you are focused on surfing then its not as hugely useful. For example, in surfing you might paddle (using your arms) for 2 minutes at a constant rate, then a burst of paddling (maybe to get over a wave), then a rest, then a burst of paddling to catch a wave. Whereas jogging 5km is just a constant rate of low intensity effort mostly using your legs.
However, if you can't already jog 5km then training until you can is going to result in improvement and is worth doing. Its part of establishing the 'base' of fitness that you need.
Your swimming routine looks much more useful for surfing, although you have a lot of warm up! Perhaps have 8x25m warm up and then 8 x 25m block of fast but not sprint without stopping; then your sprints. Obviously try to keep the rest between the sprints as short as possible.
Yoga is good.
What you dont have is any strength exercises. Circuit training is really just another cardio effort. Weights will help you get stronger and lose weight (fat, anyway) and, if you keep rest periods short, also helps aerobic ability a bit. Its also very
useful for surfing - both in terms of improving surfing and injury preventation.
After maybe 12 - 24 months of strength exercise, you can start specialising in surfing specific exercises if you want, but just start off with a basic 'all body' program. There are a zillion on google, but if you don't know how to use weights then its definitely worth getting someone to teach you the main exercises and write you a program. Low to medium reps (a weight you can only lift no more than 10 times).
Do not be 'scared' of weights! Have a read of this article (http://www.t-nation.com/free_online_art ... l_to_train
), which is obviously designed for men about getting women to go to the gym - so isnt the best article on the web, but I was just co-incidentally reading it and it covers a lot of issue. Dont forget to read the comments as well (or google to find a better article!).
So if you asked me to design your program and you wanted to focus on exercises useful for surfing, rather than general all round fitness, I would say
1. once you can jog 5km, stop jogging (unless you really enjoy it, but just do it 1x per week)
2. replace jogging with 2X per week fullbody weights/strength program (subject to back clearance). After 12-24 months, if you want, think about skewing your program towards a surfing related routine
3. things like 25m sprints, tabata (google it) and skipping - high intensity exercise - will keep your aerobic fitness up, you can usually fit them in at the end of a weight session or as a 20 min session
4. keep swimming and doing yoga
5. keep surfing
6. do a lot of reading on fitness and exercise programs for women, that focus on strength and weights, to teach and guide yourself. There is more than enough free stuff on the internet.
Hope that doesnt sound too preachy!