Seems I have come down with shin splints for the first time since I started training for the Royal Marines six months ago, and so close to my PRMC on Sept 27th, too

Looks like I ain't the only one either, which is a greater shame!
Anyway, over the last few weeks I've been feeling 'extremely' fatigued to the extent where it is difficult to even train at all. In fact, some days it feels hard just walking around/climbing stairs. I also keep getting dizzy spells now and again when I stand up (maybe normal, but something new for me) and my left arm tingles quite regularly.
I've seen my GP, and after a thorough check up (inc testing for diabetes, etc), she gave me the all clear.
Basically, this is starting to really tick me off now, because its really affecting my training (done nothing for the last 3-4 days and still feel the same). I have been through everything, nutrition, rest, etc, etc.
Just wondering if anyone else has had these symptoms and how they overcame them. I'm not looking for an online diagnosis, already seem my GP, but even after searching Google for the past '2hrs', I am still none the wiser on what could be causing these symptoms. I need to sort it out soon and get back in to 'quality' training.
Anyway, thanks for any advice.
Ayrey